I had a problem with #Misskey and its handling of the `actor` property of activities. It wasn't handling a format for that property that is defined in the Activity Streams 2.0 spec. I changed my code to be compatible (be conservative in what you send, as the #PostelPrinciple suggests) and made a PR on the Misskey codebase to make sure it could handle that format in the future from other software (be liberal in what you accept). Let's hope it gets merged!