The URL triggering this error looks pretty normal Bandcamp URL.
Looking at corresponding code at https://github.com/metabrainz/musicbrainz-server/blob/3b0b2cf9a932191ae8303c71ec143df60a25053e/root/static/scripts/edit/externalLinks.js#L1674

`su.pr` should have its dot escaped in the build regex, it isn't so it matches 'surpr' at the start of URL.
But also it seems to me it should be stricter about the end of the URL.