Can't add device

I am trying to add a new device but I am getting this error.
Yesterday everything was working normally, but after deleting a user this error occurred.

Cannot add or update a child row: a foreign key constraint fails (`tracker_x`.`tc_user_device`, CONSTRAINT `fk_user_device_userid` FOREIGN KEY (`userid`) REFERENCES `tc_users` (`id`)) - SQLIntegrityConstraintViolationException (... < QueryBuilder:461 < DatabaseStorage:77 < DataManager:258 < ...)

The error seems to indicate that you're trying to add a device to a deleted user, which would obviously fail.

I am trying to add inside an admin user, I think it should work normally. I cannot find where it is specified for which user I am creating the device.

What kind of admin user? Service account?

YES, an admin type account

Please carefully read my question. You have not answered it.

I created a user, which I gave admin privileges to. Within that user I add new devices, but from today that error appears.

OK, so it's a admin, but not a service account admin. Then I don't know how you got to this situation.