Symptoms
Domain is registered with EURid. Attempt to update contact details fails:
Voice extension information is not supported.
Cause
Phone extension is specified for the user's contacts, but EURid does not support phone extensions.
Resolution
Remove phone extension from the user's contacts. Contact EURid to submit a request to ignore phone extension if it is passed.
From BA side there is also a feature request with id #PBA-80141 ("Cut voice extension for the registrars that do not support it"), but sending the voice extension corresponds to RFC: