I'm currently in a Developer Sandbox trying to get the "External Services" to work. I have gone through the TrailHead and had it working with the resources I was supplied but once I try to use the actual API schema we need I get the error “Error encountered while saving External Registration. Please try again later.” which doesn't give me much to go off. I have tried raising the case with Salesforce and asking this question on other sites to no avail. https://salesforce.stackexchange.com/questions/309320/while-trying-to-use-the-external-sevices-i-get-the-error-error-encountered-whil?noredirect=1#comment463197_309320 (https://salesforce.stackexchange.com/questions/309320/while-trying-to-use-the-external-sevices-i-get-the-error-error-encountered-whil?noredirect=1#comment463197_309320)

Just to confirm I have created a "Named Credential" and added the corresponding domain to the "Remote Site Settings".

The Steps to reproduce the error are:

1) From Setup, enter Remote Site Settings in the Quick Find box, then select Remote Site Settings.
Click New Remote Site.
Remote Site Name, use FindAnApprenticeshipAPIURL.
Remote Site URL https://apis.apprenticeships.sfa.bis.gov.uk.

2) From Setup, enter Named Credentials in the Quick Find box, then select Named Credentials.
Click New Named Credential.
Label, use FindAnApprenticeshipNamedCred.
URL, use https://apis.apprenticeships.sfa.bis.gov.uk/manage-vacancies-sandbox/v1/apprenticeships.

3) From Setup, enter External Services in the Quick Find box, then select External Services.
Click Add an External Service.
External Service Name, use FindAnApprenticeshipExService.
Select a Named Credential, select FindAnApprenticeshipNamedCred.
Select Service Schema Complete JSON. Then paste the schema information from "https://developers.apprenticeships.education.gov.uk/docs/services/eebd1522767f4f1fbdfe51bd7010aa7e/export?DocumentFormat=Swagger":

{
"swagger": "2.0",
"info": {
"title": "Manage vacancies API (Sandbox)",
"version": "1.0",
"description": "Manage vacancies API (Sandbox)"
},
"host": "apis.apprenticeships.sfa.bis.gov.uk",
"basePath": "/manage-vacancies-sandbox",
"schemes": [
"https"
],
"securityDefinitions": {
"apiKeyHeader": {
"type": "apiKey",
"name": "Ocp-Apim-Subscription-Key",
"in": "header"
},
"apiKeyQuery": {
"type": "apiKey",
"name": "subscription-key",
"in": "query"
}
},
"security": [
{
"apiKeyHeader": []
},
{
"apiKeyQuery": []
}
],
"x-servers": [
{
"url": "https://apis.apprenticeships.sfa.bis.gov.uk"
},
{
"url": "https://apis.apprenticeships.education.gov.uk"
}
],
"paths": {
"/v1/apprenticeships": {
"post": {
"description": "The apprenticeship operation creates an apprenticeship vacancy using the specified values.\r\n\r\n#### Restricted values ####\r\n\r\nThese fields will only accept specific values as listed below:\r\n* ApplicationMethod\r\n - Online\r\n - Offline\r\n* LocationType\r\n - OtherLocation\r\n - EmployerLocation\r\n - Nationwide\r\n* DurationType\r\n - Weeks\r\n - Months\r\n - Years\r\n* WageType\r\n - CustomWageFixed\r\n - CustomWageRange\r\n - NationalMinimumWage\r\n - ApprenticeshipMinimumWage\r\n - Unwaged\r\n - CompetitiveSalary\r\n - ToBeSpecified\r\n* WageUnit\r\n - NotApplicable\r\n - Weekly\r\n - Monthly\r\n - Annually\r\n* TrainingType\r\n - Framework\r\n - Standard\r\n\r\n#### Validation rules ####\r\n\r\nWhen creating a vacancy the following rules must be considered. \r\n1. All values are required to be populated except in the following cases:\r\n\r\n* For all vacancies these values are optional\r\n - ContactName\r\n - ContactEmail\r\n - ContactNumber\r\n - ThingsToConsider\r\n\r\n* For an Online vacancy\r\n - SupplementaryQuestion1 and SupplementaryQuestion2 are optional\r\n - ExternalApplicationUrl and ExternalApplicationInstructions must be empty\r\n\r\n* For an Offline vacancy\r\n - ExternalApplicationInstructions is optional\r\n - SupplementaryQuestion1 and SupplementaryQuestion2 must be empty\r\n\r\n* When LocationType is EmployerLocation or Nationwide \r\n - Location is not required.\r\n\r\n* When LocationType is OtherLocation \r\n - Only Address1, Town and Postcode are required\r\n - All other address fields are optional\r\n\r\n* When WageType is CustomWageFixed\r\n - WageTypeReason must be empty\r\n - WageUnit must be a value other than NotApplicable\r\n - MinWage and MaxWage must be empty\r\n - FixedWage must be greater than or equal to the Apprenticeship minimum wage \r\n\r\n* When WageType is CustomWageRange\r\n - WageTypeReason must be empty\r\n - WageUnit must be a value other than NotApplicable\r\n - MinWage must be greater than or equal to the Apprenticeship minimum wage \r\n - MaxWage must be greater than MinWage\r\n - FixedWage must be empty\r\n\r\n* When WageType is NationalMinimumWage or ApprenticeshipMinimumWage\r\n - MinWage, MaxWage, FixedWage and WageTypeReason must be empty\r\n - WageUnit must be NotApplicable\r\n\r\n* When WageType is Unwaged, CompetitiveSalary or ToBeSpecified\r\n - FixedWage, MinWage and MaxWage must be empty\r\n - WageUnit must be NotApplicable\r\n\r\n* When TrainingType is Framework\r\n - TrainingCode should be in format ###-##-##\r\n\r\n* When TrainingType is Standard\r\n - TrainingCode should be a numeric value no greater than 9999\r\n\r\n* Text fields will take a maximum of 4,000 characters except for the following\r\n - Title = 100\r\n - ShortDescription = 350\r\n - ContactName = 100\r\n - ContactEmail = 100\r\n - AddressLine = 300\r\n - Town = 100\r\n - WageTypeReason = 240\r\n - WorkingWeek = 250\r\n\r\n* Additional rules\r\n - Title must include the word ***apprentice***\r\n - HoursPerWeek must be between 16 and 48 inclusive\r\n - ExpectedDuration must be a minimum of 1 year, 12 months or 52 weeks depending on the value of DurationType selected\r\n - NumberOfPositions must not exceed 5,000\r\n\r\n#### Error codes ####\r\n\r\nThe following error codes may be returned when calling this operation if any of the vacancy values \r\nspecified fail validation:\r\n\r\n| Error code | Explanation |\r\n| ----------- | ------------------------------------------- |\r\n| 31000 | Invalid Request body |\r\n| 31001 | Invalid Title |\r\n| 31002 | Invalid Short description |\r\n| 31003 | Invalid Long description |\r\n| 31004 | Invalid Application closing date |\r\n| 31005 | Invalid Expected start date |\r\n| 31006 | Invalid Working week |\r\n| 31007 | Invalid Hours per week |\r\n| 31008 | Invalid Wage type |\r\n| 31009 | Invalid Wage type reason |\r\n| 31010 | Invalid Wage unit |\r\n| 31011 | Invalid Fixed wage |\r\n| 31012 | Invalid Min wage |\r\n| 31013 | Invalid Max wage |\r\n| 31014 | Invalid Expected duration |\r\n| 31015 | Invalid Duration type |\r\n| 31016 | Invalid Location type |\r\n| 31017 | Invalid Location Address line 1 |\r\n| 31018 | Invalid Location Address line 2 |\r\n| 31019 | Invalid Location Address line 3 |\r\n| 31020 | Invalid Location Address line 4 |\r\n| 31021 | Invalid Location Address line 5 |\r\n| 31022 | Invalid Location Town |\r\n| 31023 | Invalid Location Postcode |\r\n| 31024 | Invalid Number of positions |\r\n| 31025 | Invalid Provider's Ukprn |\r\n| 31026 | Invalid Employer's Edsurn |\r\n| 31027 | Invalid Provider site's Edsurn |\r\n| 31028 | Invalid Contact Name |\r\n| 31029 | Invalid Contact Email |\r\n| 31030 | Invalid Contact Number |\r\n| 31031 | Invalid Training Type |\r\n| 31032 | Invalid Training Code |\r\n| 31033 | Invalid Desired skills |\r\n| 31034 | Invalid Desired personal qualities |\r\n| 31035 | Invalid Desired qualifications |\r\n| 31036 | Invalid Future prospects |\r\n| 31037 | Invalid Things to consider |\r\n| 31038 | Invalid Training to be provided |\r\n| 31039 | Invalid Application method |\r\n| 31040 | Invalid Supplementary question 1 |\r\n| 31041 | Invalid Supplementary question 2 |\r\n| 31042 | Invalid External application url |\r\n| 31043 | Invalid External Application Instructions |\r\n| 31044 | Invalid Is Employer Disability Confident |\r\n| 31045 | Invalid Location Additional Information |\r\n| 31046 | Invalid Employer Description |\r\n| 31047 | Invalid Employer Website Url |",
"operationId": "CreateApprenticeshipVacancy",
"summary": "CreateApprenticeshipVacancy",
"tags": [
"Apprenticeships"
],
"parameters": [
{
"name": "createApprenticeshipParameters",
"in": "body",
"schema": {
"$ref": "#/definitions/CreateApprenticeshipParameters"
}
}
],
"consumes": [
"application/json",
"text/json",
"application/xml",
"text/xml",
"application/x-www-form-urlencoded"
],
"produces": [
"application/json",
"text/json",
"application/xml",
"text/xml"
],
"responses": {
"200": {
"description": "OK",
"schema": {
"$ref": "#/definitions/CreateApprenticeshipResponse"
}
},
"400": {
"description": "Failed request validation",
"schema": {
"$ref": "#/definitions/BadRequestContent"
}
},
"401": {
"description": "Invalid provider ukprn",
"schema": {
"$ref": "#/definitions/StringContent"
}
}
}
}
}
},
"definitions": {
"CreateApprenticeshipParameters": {
"type": "object",
"properties": {
"title": {
"type": "string"
},
"shortDescription": {
"type": "string"
},
"longDescription": {
"type": "string"
},
"desiredSkills": {
"type": "string"
},
"desiredPersonalQualities": {
"type": "string"
},
"desiredQualifications": {
"type": "string"
},
"futureProspects": {
"type": "string"
},
"thingsToConsider": {
"type": "string"
},
"trainingToBeProvided": {
"type": "string"
},
"applicationMethod": {
"enum": [
"Online",
"Offline"
],
"type": "string"
},
"supplementaryQuestion1": {
"type": "string"
},
"supplementaryQuestion2": {
"type": "string"
},
"externalApplicationUrl": {
"type": "string"
},
"externalApplicationInstructions": {
"type": "string"
},
"expectedDuration": {
"format": "int32",
"type": "integer"
},
"durationType": {
"enum": [
"Weeks",
"Months",
"Years"
],
"type": "string"
},
"applicationClosingDate": {
"format": "date-time",
"type": "string"
},
"expectedStartDate": {
"format": "date-time",
"type": "string"
},
"workingWeek": {
"type": "string"
},
"hoursPerWeek": {
"format": "double",
"type": "number"
},
"wageType": {
"enum": [
"CustomWageFixed",
"CustomWageRange",
"NationalMinimumWage",
"ApprenticeshipMinimumWage",
"Unwaged",
"CompetitiveSalary",
"ToBeSpecified"
],
"type": "string"
},
"wageTypeReason": {
"type": "string"
},
"wageUnit": {
"enum": [
"NotApplicable",
"Weekly",
"Monthly",
"Annually"
],
"type": "string"
},
"minWage": {
"format": "double",
"type": "number"
},
"maxWage": {
"format": "double",
"type": "number"
},
"fixedWage": {
"format": "double",
"type": "number"
},
"locationType": {
"enum": [
"OtherLocation",
"EmployerLocation",
"Nationwide"
],
"type": "string"
},
"location": {
"$ref": "#/definitions/Location"
},
"numberOfPositions": {
"format": "int32",
"type": "integer"
},
"employerEdsUrn": {
"format": "int32",
"type": "integer"
},
"providerSiteEdsUrn": {
"format": "int32",
"type": "integer"
},
"contactName": {
"type": "string"
},
"contactEmail": {
"type": "string"
},
"contactNumber": {
"type": "string"
},
"trainingType": {
"enum": [
"Framework",
"Standard"
],
"type": "string"
},
"trainingCode": {
"type": "string"
},
"isEmployerDisabilityConfident": {
"type": "boolean"
},
"employerWebsiteUrl": {
"type": "string"
},
"employerDescription": {
"type": "string"
}
}
},
"Location": {
"type": "object",
"properties": {
"addressLine1": {
"type": "string"
},
"addressLine2": {
"type": "string"
},
"addressLine3": {
"type": "string"
},
"addressLine4": {
"type": "string"
},
"addressLine5": {
"type": "string"
},
"postcode": {
"type": "string"
},
"town": {
"type": "string"
},
"additionalInformation": {
"type": "string"
}
}
},
"CreateApprenticeshipResponse": {
"type": "object",
"properties": {
"vacancyReferenceNumber": {
"format": "int32",
"type": "integer"
}
}
},
"BadRequestContent": {
"type": "object",
"properties": {
"requestErrors": {
"type": "array",
"items": {
"$ref": "#/definitions/BadRequestError"
}
}
}
},
"BadRequestError": {
"type": "object",
"properties": {
"errorCode": {
"type": "string"
},
"errorMessage": {
"type": "string"
}
}
},
"StringContent": {
"type": "object",
"properties": {
"headers": {
"type": "array",
"items": {
"$ref": "#/definitions/KeyValuePair[String,IEnumerable[String]]"
},
"readOnly": true
}
}
},
"KeyValuePair[String,IEnumerable[String]]": {
"type": "object",
"properties": {
"key": {
"type": "string",
"readOnly": true
},
"value": {
"type": "array",
"items": {
"type": "string"
},
"readOnly": true
}
}
}
},
"tags": []
}

4) Press Save.

Then get the error "Error encountered while saving External Registration. Please try again later."

Any help will be much-appreciated thankyou.