It's a shame, as I think the 3WordAuto implementation of W3W has much greater value to MB owners with MBUX systems than their standard app.I get the same in the UK
While I'm glad it's not specific to me, I'm sorry that it isn't working for you either in the UK, with a UK account, on a UK-developed app.
I imagine it must be happening to others, as well. Maybe if everybody who has this issue leaves a review and contacts their tech support, they'll figure out the problem and fix it.
I already left a review, and I'm about to hit send on an email, as well. I'll let you know if they have a fix for me. It may work for you, as well.