IBM - MAS : - Error AIUCO1026E: Unable to create user with id=, since it is already taken by a previously-deleted user.

The only way to restore the user or permanently delete the user from MAS is to update or delete the document in the mongoDB database.

Steps

1- Connect to the mongoDB shell 

https://www.ibm.com/support/pages/how-open-mongo-shell-mas-mongodb

2- List the databases:

show dbs

3- Use the mas core database:

use mas_<mas instance id>_core

4- find the user you want to restore or delete:

db.User.find({"_id" : "testuser"})

When the user is deleted, the document will end with the deleted information, i.e. user who deleted the record and the time of deletion, for example:

"deleted" : { "id" : "masadmin", "timestamp" : "2023-11-28T09:56:29.840785" }

You can then either restore the user or remove it from the database

To restore the user, execute the following command:

db.User.update({username: "testuser"},{$unset: {deleted:""}})

Once the command is executed, the user is visible again in MAS, however it is not visible in Manage.

An update to the user in MAS will lead to a syncronization failure with Manage. You need to reactivate the use in Manage.

To remove the user, execute the following command:

db.User.deleteone({username: "testuser"})

If you create a new user with the id of the user that you deleted, the synchronization with Manage will fail, you will have to reactivate the user in Manage.

The instructions to reactivate the user in Manage are here:

https://www.ibm.com/support/pages/reinstating-deleted-person-record-maximo

NOTE: removing the user from the database is permanent, it is recommended to have a working backup before attempting such operation. 

Reference link : https://www.ibm.com/support/pages/node/7085329