Revolut is giving me “Declined. Unsupported merchant” for transactions through my Curve card with Revolut as the funding card.
The merchant in this case isn’t Curve, it’s the ‘shop’ where you buy. So Curve might be blocking this shop (or the MCC this shop is using).
I would be very surprised if Curve would be blocking Revolut, if it is, the message you are receiving is incorrect as Revolut isn’t the merchant.
Edit: I might have misunderstood your post, you are suggesting that Revolut is not allowing transactions through Curve anymore. For Revolut Curve is actually the merchant.
For most transactions Curve does send the original MCC though, so it also might be that you are trying to use your Revolut card (through Curve) for a MCC that isn’t allowed by Revolut.
But still I would be surprised if Revolut would no longer support Curve.
Where do you receive the message “Declined. Unsupported merchant”, if in the Curve app the 1st paragraph of my post applies, if in the Revolut app the 2nd paragraph of my post applies.
Curve + revolut worked for me Monday