While creating a test user in my app in Facebook developer, I get this error:
The ability to create test users is disabled temporarily
Documentation related to create "Test Users" is currently showing the next message:
Even if you try to add a user it may tell you that you must delete one to add a new one.
So, the ability to create test users is disabled temporarily in this section of Facebook.
Alternatively, you can add a user, and assign the "Tester" role, go to "App roles" > "Roles", select the role "Tester" and add a Facebook user :
After registering the user as a "Tester", go to the user requests section:
https://developers.facebook.com/settings/developer/requests/
then accept the request, to have a "Tester" user for your Facebook App: