Read metadata doesn't seem to work with External Services

[braveMoose]

Hi team,

I'm trying to get info from our external services via the readMetadata method, but I'm getting an error message along the way.

The code :
MetadataService.MetadataPort service = MetadataService.createService();
system.debug(service.readMetadata('ExternalServiceRegistration', new String[]{'EXTSRV001'}));

The error message :
Line: 13500, Column: 1
System.CalloutException: Web service callout failed: Unable to parse callout response. Apex type not found for element namedCredentialReference

Could you please let me know if there would be a workaround ?

Thanks for the great tool you're providing !

Ariane