Hi sajin,
First you have to check the ONLY privilege. If you want to create a user into the back-end system, you should attache the PRIV:back-end-system-name:ONLY to the user.
1. Check if you have created the privilege
2. Check the setting of the privilege
3. Check the master privilege for the respective repository(master privilege=ONLY privilege)
4. Assign the ONLY privilege to the user
Kind Regards,
Simona