In PBA-S 4.3.3 we are trying to create new extended attribute for Plesk subscription objects. This is possible according to Provider's Guide:
If it is needed to add some custom or specific information to a subscription profile, it is possible to do this by configuring editable fields within a subscription settings. Such additional fields are called extended attributes. Extended attributes can be added to subscription using Parallels Business Automation API. For details refer to the Parallels Business Automation SDK. Having been added, extended attribute(s) are grouped within a subscription properties, Account Director > Subscription Manager > Subscription, select subscription, switch to Ext. Attributes tab.
Everything is done according to the PBA-S SDK instructions. But the problem is that the we can't see/edit the "Ext. Attributes" tab anywhere in the Subscription view in PCC:
Top > Account Director > Subscription Manager > Subscriptions > <SUBSCRIPTION_NAME>
Extended attributes can be added for subscription using PBA-S 4.3 SDK information, but the tab is not visible in GUI.
The problem has been fixed since version 4.3.4. Bug is PBAS-28986.
Consider upgrading PBA-S to the most recent version.