Genre Error on DOI Submission ECMLG


I have 68 articles from one Proceedings/Journal that are Failing to deposit at Crossref.

These articles sit in an OJS repository and we are using the OJS Crossref plugin to submit new DOIs via XML.

The other 14 of our 15 Proceedings / Journals are working fine.

Just one gives the following “genre” error.

Registration was not successful! The DOI registration server returned an error: ‘ISSN “2048903X” has already been assigned, title/issn: European Conference on Management Leadership and Governance/2048903X is assigned to another genre: CONFERENCE_PROCEEDING_SERIES (403 Forbidden)’.

The ECMLG Online ISSN is set to 2048-903X

I have double checked the ISSN and Title.

Please can someone assist and let me know how to resolve??