Sounds like your instance has blocked the IP of your VPN.
It's lemmy.world blocking the API calls when you use VPN. Bring it up with the admins, nothing boost can do.
Sidenote, that's something I love about the Fediverse. Something server-side you don't like? Ask the admins, who are real people who do this as a (semi-paid) hobby.
Don't like something about BlueSky, Threads, etc.? Talk to Customer Service, and they'll be sure to round-file your complaint right away!
I have the exact same issue. Someone is blocking. I have a dedicated IP and still get hit.
I assume it's not Boost.
I think I heard that is a Lemmy World thing. I guess it cuts down on trolls and spam because you have to connect from a real ip
If you change IPs you might stumble on one that isn't blocked. Many websites block VPNs so if you have problems online check if it's the VPN.
Boost For Lemmy
Community of the Android app Boost for Lemmy