Redmine integration does not work: Authentication error


I am using Sentry’s hosted service ( and have activated the Redmine integration. After entering the URL for the API and the API key of the user who will make the tickets, I get an authentication error.

The URL and the API key are correct, I can use them in a regular browser to retrieve, e.g. an issue listing.

In the Redmine loggings, I see no connection from Sentry that points to an attempt to authenticate.

What can be the issue here? Please advise.

Our Redmine version is 3.3.2.stable, running on a publicly accessible server (for our external developers).

Your help is much appreciated.

Kind regards,