Can't publish add-on Duplicate add-on ID found error

I am trying to Submit a New Add-on on uploading the add-on package
its says always “Duplicate add-on ID found” even though there is no addon with that id. even after changing the add-on id in manifest.json to something unique it always shows and error "Duplicate add-on ID found for every id.

Thank you.

Hey @webpocpluginextension, sorry to hear you’re having problems. What is the ID of the extension you are trying to submit? We can look into it on the back-end.

Separately – have you submitted an extension with this ID at any time in the past (as a self-hosted add-on, or as a new submission that was later deleted)? AMO does a case insensitive check for unique IDs at the time of a first submission; when new versions are uploaded, it does a case sensitive check on the ID to ensure it’s the same.