Hook for transmission & what images?

a) Is there a hook I could use to record that a custom post type entry has been published via ActivityPub? Background: I would like to show on the custom post type that it was published via ActivityPub. If I could also get the time of transmission and the external URL, it would be perfect.

there is no ?external url“ and there is no real time of transmission. The plugin sends the post directly to the inbox of all followers, so there might be transmission dates for every inbox. The plugin does not crosspost the content, it works like any other fediverse platform (like for example mastodon) so the external url is the same as the internal url.

b) On Mastodon, an image is displayed with the submitted posts. Which image do I have to set on a custom post type so that it is used for this? As a feature image? Why are there 3 images in the ActivityPub settings?

The plugin uses the featured image plus the images you used in the content and with the number in the settings you can define the max number of images that will be sent.

I hope this answers your questions ??

The time of transmission to the inboxes would suffice. Simply as a characteristic “was sent” or “was distributed”. Is that possible?