I donโt know anything about your environment, but I would try the SamAccountName and perhaps the email address as the username (instead of the AD username field).
EDIT: Just noticed that you have the request as raw\Text instead of raw\JSON, which would be the first thing to try.
Thanks for your reply. I sorted out the issue and its now working from me.
I was using AD\ But when i made the API-request to pull all the user details from local user then i noticed that the AD username appeared in the response as AD\.
I tried with AD\ and it worked.
I already tried with the full email-address like abc@test.com earlier but it did not work. This is why i posted my query as a help-seeker here and i am glad to notice that we actually have some help available here
I was using doamin\username (single bacslash after domain)
but the issue got fixed when i started using domain\username
(Double backslash after domain)
I donโt know why double backslash is not getting visible here . Strange !!