Hello @Shivam_Tripathi_KS,
Please indicate your version number (e.g. OJS 3.3.0-8) in your posts, as it assists others with troubleshooting. One thing you might want to do is check your Crossref (assuming Crossref is your DOI registration agency) credentials, as is suggested here: DOIs not deposited error in OJS 3.0.0 - #4 by Isabel-M
-Roger
PKP Team