Follow request from the web UI fails, even though remote user has not blocked me

[asyncmeow]

Steps to reproduce the problem

1. Go to the profile for a remote user
2. Send a follow request

Expected behaviour

The follow request should go through without any errors

Actual behaviour

The follow request fails, with the network request showing "This action is not allowed" in the response

Detailed description

I attempted to follow someone, but when I click the follow button, the follow request instantly fails. In the developer console, I see the request fails with a 403 error, saying {"error": "This action is not allowed"}. I have verified that this is not caused by the user on the remote instance blocking me (by asking them directly outside of the fediverse). Additionally, I'm not able to see any of their posts (nor can they see mine), which may be a related issue. The user in question is @theresnotime@fox.nexus, and I'm trying to follow them from @pearl@rrr.sh (or @pearl@fedi.rrr.sh if your instance does not support having a separate WEB_DOMAIN and LOCAL_DOMAIN)

Mastodon instance

fedi.rrr.sh

Mastodon version

v4.3.0-nightly.2024-03-28+glitch

Browser name and version

Firefox 123.0.1

Operating system

macOS Ventura 13.4.1

Technical details

Technical details included in the detailed description.