https://www.cnet.com/news/tinder-crashes-after-facebook-implements-data-policy/

In an attempt to prevent another Analytica-gate, Facebook on Wednesday implemented new measures to regulate the data third-party apps can use and access. Hours later, lonely hearts the world round were reporting they could no longer log in to Tinder.

To get an account on the app, prospective users need to either log in with their phone number or their Facebook account. Given the latter is quicker and allows instant access to a library of photos, which are then used to create your profile, that's the one most people go for.