Can't login to Spotify - iPhone 6 plus

[user-removed]

I've got the Spotify app on my iPhone 6 plus, which is running iOS 11.3.1.

My account is linked to my Facebook profile so when trying to login I click the "Log in with Facebook" button on the app. However the app freezes with the notification "Spotify wants to use facebook.com to sign in" comes up in the middle of the screen with three "loading" dots in the background. It will not allow me to click "continue" and the only way to then exit the app is to press the on/off button.

I have already tried turning the phone on and off and reinstalling the Spotify app but this hasn't made a difference.