Got another reply from support. Now they said that bank (underlaying card issuer) sent them code “do not honour” and thats why it was declined for Monese top-up. They suggested to contact underlaying card issuer, which is Revolut in my case.
It’s a bit weird - becouse all other purchases works with this Revolut card thru Curve. And it worked before for monese top-up via Curve. Only thing thats changed from revolut’s side - they switched clients (me also) from GB to LT. So if earlier top-up from my bank to Revolut appeared as transaction to GB, now its transaction to LT. Maybe thats the reason something got wrong (as revolut card was added to curve long ago while it was still under GB, not LT).
Also to test “fronted must be ON” suggestion from Lucas in some posts above I switched it ON and tried top-up. Transaction was still declined.
Will try to contact revolut’s support now.