In February 2019, DOAJ tightened up procedures for article uploads. This includes checks that are carried out on uploads particularly ISSN, DOI, and full text URL information.
This means that, whether uploading article XML or JSON via the API, the metadata must include the exact same ISSN value(s) as those DOAJ holds in the journal record. If a journal title has two ISSNs on its website (one ISSN for the print version and one ISSN for the online version) and DOAJ only has one, you should contact DOAJ to have the second ISSN added. If need be, the ISSN Network can be contacted to update journal metadata.