Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, We can't save this record because the “Fulfillment Creation” process failed. Give your Salesforce admin these details. This error occurred when the flow tried to create records: FIELD_INTEGRITY_EXCEPTION: Assigned To ID: id value of incorrect type: 0063i000003ZVyyAAG. You can look up ExceptionCode values in the SOAP API Developer Guide. Error ID: 990470032-165661 (-1137041356): []

Error message I'm getting:

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error while verifying this challenge. Usually this is due to some pre-existing configuration or code in the challenge Org. We recommend using a new Developer Edition (DE) to check this challenge. If you're using a new DE and seeing this error, please post to the developer forums and reference error id: PSACFGLO

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, We can't save this record because the “Fulfillment Creation” process failed. Give your Salesforce admin these details. This error occurred when the flow tried to create records: FIELD_INTEGRITY_EXCEPTION: Assigned To ID: id value of incorrect type: 0063i000003ZVyyAAG. You can look up ExceptionCode values in the SOAP API Developer Guide. Error ID: 990470032-165661 (-1137041356): []