Do you to the Oauth problem affecting many third-party integrations, simple rule builder will not work for UK account at this time. Nothing you can do about it it’s an authorisation issue on the SmartThings side.
SmartThings has said they know about it and are working on it but it’s quite a large problem to fix. When it is fixed, many different third-party integration should become available again.
The issue is being tracked in the following thread: