A service user cannot be created:
User with login 'firstname.lastname@example.org' already exists
At the same time, checking the presence of such login at TOP > System > Users > Service users, nothing can be found.
A possible cause: during the first user creation, the operation was interrupted (e.g. by services restart) and did not complete successfully, but part of the data have already been added to the system. Such behavior is recognized as a software issue APS-43574.
The mentioned software-related issue was fixed in OA 7.3. Please consider upgrade. Contact your Technical Account Manager or Pooled Technical Associate Team (email@example.com) in order to discuss possible workaround for APS-43574.