Ok I have tried to get the new 1.0 version of the ActivityPub plugin for WordPress working, but unfortunately it still has the same bug as 10 months ago when I last tried this (ref https://wordpress.org/support/topic/webfinger-endpoint-unavailable/). @pfefferle not sure if you have any further suggestions, but it seems like WP sites hosted on Hostinger still cannot use this plugin on Mastodon :(
@ricmac I already had contacted hostinger and the last message I received was "we are working on it". sadly this is an issue that I can't solve on plugin level and WebFinger is something that is required at least from Mastodon.