This was not a problem with the old OAuth 1.0 "PrivateApp" but since that was deprecated finally a couple of weeks ago, we just migrated our code to OAuth 2.0 and some of our Contacts were getting updated but a couple broke the API will give you a validation error if you try to save a different format for the contact. In the USA, it is fairly common for a Contact that use their SSN (xxx-xx-xxxx) to "upgrade" to a EIN format (xx-xxxxxxx) https://community.xero.com/developer/discussion/13402153
This was not a problem with the old OAuth 1.0 "PrivateApp" but since that was deprecated finally a couple of weeks ago, we just migrated our code to OAuth 2.0 and some of our Contacts were getting updated but a couple broke the API will give you a validation error if you try to save a different format for the contact. In the USA, it is fairly common for a Contact that use their SSN (xxx-xx-xxxx) to "upgrade" to a EIN format (xx-xxxxxxx) https://community.xero.com/developer/discussion/13402153