From wheeljack's comment to ---MBS-8390---:

I am no longer able to add Bandsintown links to the artist page as of today.
Whenever I try to do that, I now get:
"This URL is not allowed for the selected link type, or is incorrectly formatted."

Here is the link I tried to add:
http://www.bandsintown.com/Altocamet
to this artist:
https://www.musicbrainz.org/artist/f9efcd8f-eebe-4b26-8665-2c1051ffd584

This is true of both the live server as well as beta.

I see what happened, I was adding links with a leading "www", for example http://www.bandsintown.com/altocamet
This is because that's the link that shows up when you search for that artist from google, for example:
https://www.google.com/#q=bandsintown+altocamet

When I removed the "www" to http://bandsintown.com/altocamet, it got added correctly, it even corrected the http:// to https://
I think the solution for this would be to automatically strip the "www" since I am sure other users will make the same mistake that I did.

Similarly, the "m" can be stripped from http://m.bandsintown.com/Altocamet