Hello @juanf.csic,
Just a quick note to say that the issue as well as a potential solution has been pinpointed here: Trying to register an article with the DOAJ plugin throws an error : new DOAJ API version · Issue #6389 · pkp/pkp-lib · GitHub
We’re looking into seeing if the new DOAJ is backwards-compatible and if, so, will likely issue an update to the DOAJ plugin.
Best regards,
Roger