Hello,
I now get an error when trying to create a new account or to re-allow permission
and I don’t know what is the meaning of that error
application ID K6B28yo6zeWi1SYCmg14WQ
Can you help me please ?
FredG
Non multiunit aware applications aren’t supported any more with Square APIs. As a partner you should have received notifications about migration, deprecation, and notices of usage prior to retirement of this functionality.
Do you still have customers using the application you provided? 
What’s your application ID?
Okay, that application isn’t multiunit aware. You’ll have to create a new application in the Developer Dashboard to generate a multiunit aware application. Then you’ll have to migrate all sellers to the new application to access the functionality.
Yes, existing sellers will need to OAuth to the new app.