I’m working on an an automation framework and I’m trying to use the activitypub protocol to send a message to a user’s mailbox.

I am following this guide

which is quite old. I’ve set up my webfinger and my user account page and that is now discoverable by the fediverse

However I cannot figure out how to send a PM to a specific mailbox. The payload and url provided in that guide just return 400.

Can anyone assist?

If you know of a better community to ask, please let me know.