Trying to add a series to Sonarr from a search in NZB360 Pro - can connect to Sonarr fine via primary address, but series add fails with "couldn't add series try again {methodnotallowed}".

Sonarr Ver. is running on a local machine, portforwarded outside successfully, NZB360 is connected via URL:port in Primary Connection Address + API key and the test connection response is green.

Nothing appears in Sonarr logs at TRACE level, and I can add series just fine from the webui. Tried adding authentication to the beginning of the UR, and tried local connection (both tested green_ but no change.
Any ideas what this message means?