Hello,

here is what i did to use the Apex callout in my flow.

I use it to manage the multilingual in the flow: the flow is unique and the translations of the questions are stored in the Custom Settings (Flow_Display_Text_2__c  object)

The Apex class called by the Apex callout (based on some code found in the doc (but i don't find the url back)) :-(

global class TranslationsFlow implements Process.Plugin { 

public class TranslationException extends Exception {}
  
global Process.PluginResult invoke(Process.PluginRequest request) { 
        // Get the subject of the Chatter post from the flow  
    
        String lang = (String) request.inputParameters.get('lang');
        String process = (String) request.inputParameters.get('process');
        
        Flow_Display_Text_2__c[] res = 
            [SELECT AAA_Q_BP_Number__c, AAA_POM_Allowed__c, AAA_POM_Error__c
            FROM Flow_Display_Text_2__c
            WHERE Name =: lang];
            
        if (res.size() != 1) throw new TranslationException('System error: translation '+lang+' not supported');
 
        // return to Flow  
    
        Map<String,String> result = new Map<String,String>();
        result.put('AAA_Q_BP_Number__c',res[0].AAA_Q_BP_Number__c); 
        result.put('AAA_POM_Allowed__c',res[0].AAA_POM_Allowed__c); 
        result.put('AAA_POM_Error__c',res[0].AAA_POM_Error__c); 
        return new Process.PluginResult(result); 
    } 

 and other function i didn't change (from the documentation)

    // Returns the describe information for the interface  
    
    global Process.PluginDescribeResult describe() { 
        Process.PluginDescribeResult result = new Process.PluginDescribeResult(); 
        result.inputParameters = new 
           List<Process.PluginDescribeResult.InputParameter>{ 
               new Process.PluginDescribeResult.InputParameter('subject', 
               Process.PluginDescribeResult.ParameterType.STRING, true) 
            }; 
        result.outputParameters = new 
           List<Process.PluginDescribeResult.OutputParameter>{ }; 
        return result; 
    }
}

In my flow, i've a Value Table for input "VT Translations Input" with 2 keys 'lang' and 'process'. And another Value Table for output "VT Translations Output" with 3 keys 'AAA_Q_BP_Number__c', 'AAA_POM_Allowed__c' and 'AAA_POM_Error__c' (defined explicitly in the Value Table)

Then I've just to add the Apex callout with input

- Apex classname : TranslationsFlow  (name of the class hereabove)

- Input Values : VT Translations Input

and output:

- Output values : VT Translations Output

It works fine, i've no error.

Hope it helps.

Cheers