Unable to connect Mastodon v3.5.2 to Nextcloud

Every time I try to connect my mastodon account using this app, and I click “authorize” on mastodon, nextcloud returns with this:

Mastodon OAuth access token could not be obtained: Error getting OAuth access token Client error: `POST https://%40soulfire@thetooniverse.xyz/oauth/token` resulted in a `401 Unauthorized` response:
{"error":"invalid_client","error_description":"Client authentication failed due to unknown client, no client authenticat (truncated...)

This has happened with other instances as well, do I need to make an app on my mastodon account to use it or something?