I have a practical question. I go on vacation to the US for 2 weeks. There I´ll use my current phone (European Sim Card with european number) with a US-Prepaid-Sim (US Sim with US number). Are there any problems with that using my revolut account in that time? After the two weeks i´ll have my old sim again in the phone.
You should have no problems. If you get logged out, then just pop your EU sim back in to receive your login code Have a nice trip!
Some features like adding a new recipient for a transfer rely on 2 factor authentication via texts sent to that number. If you’re not going to use features like this, you should not run into problems.
(And don’t fully log out. You need again a text sent to your number to log in again.)
If you need to access the app, to unblock or freeze the card, receive payment notifications, top up/check balance for example, you would need full access to your UK? phone where the app is installed.
I put my US sim in a spare phone and leave my UK phone as it is.
You do not. You just have to be logged in. It won’t log you out because you change the sim.