Can't post from Ulysses anymore, please help!

Hello,
It seems I can no longer post from Ulysses. The new post images do appear in the “Uploads” section, but the new posts do not show up anywhere.
I receive the following error message: “Unable to publish. There was a problem connecting to the server. Please contact support for assistance in resolving this issue” (I’m translating this from Italian, so the actual English text may differ).
The log isn’t showing any error messages.
How can I troubleshoot this, and do you think this is an issue with Micro.blog or with Ulysses? I even created a new API key and entered it into Ulysses, but that didn’t help.
Thanks!

In the meantime, I inspected the HTTP requests from Ulysses. As you can see, posting to micro.blog/micropub gives a “500 - Internal server error” message. Hope this helps.

Thank you very much Manton for your fix, it’s working great now!

Just for completeness for others, we did have an issue with posting from some apps including Ulysses, and it’s fixed. Thanks!