Relay isn't following Mastodon instances back - Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)

Hello,

Recently, I have failed to subscribe a Mastodon to this relay and have received the following messages in debug mode:

[2023-07-10 21:03:26,505] VERBOSE: Added inbox to database: https://mastodon.vn.ua/inbox
[2023-07-10 21:03:26,539] VERBOSE: Sending "Accept" to https://mastodon.vn.ua/inbox
[2023-07-10 21:03:26,573] VERBOSE: Received error when pushing to https://mastodon.vn.ua/inbox: 401
[2023-07-10 21:03:26,573] VERBOSE: b'{"error":"Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)"}'
[2023-07-10 21:03:44,504] INFO: 195.206.232.215 "POST /inbox HTTP/1.1" 202 176 "http.rb/5.1.1 (Mastodon/4.1.4; +https://mastodon.vn.ua/)"
[2023-07-10 21:03:44,505] VERBOSE: New "Follow" from actor: https://mastodon.vn.ua/actor
[2023-07-10 21:03:44,539] VERBOSE: Sending "Accept" to https://mastodon.vn.ua/inbox
[2023-07-10 21:03:44,599] VERBOSE: Received error when pushing to https://mastodon.vn.ua/inbox: 401
[2023-07-10 21:03:44,599] VERBOSE: b'{"error":"Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)"}'

Any thoughts?