Yes, using the latest build and have rebooted the core. Also uninstalled/reinstalled both Roon and Tidal.
It’s weird, when I go to settings>services>tidal the field where i can log in to Tidal allows me to put my account name in, but the “continue” button remains greyed out. I can hit return, and that’s when I get the OAuth2 message
Thanks for your help everyone, it’s solved, although I have no idea why it worked.
My roon core is on a PC and I use an ipad as a roon remote. I reinstalled the roon remote on the ipad and connected to Tidal via that (instead of via the PC) and now everything works perfectly again.