I confirm everything is working fine now! Both my unicredit debit card ando also my ING mastercard work like a charm!!! Finally 
Yes, I have just topped up using Italian Bancoposta mastercard.
For me its still not working, trying to use a Unicredit Mastercard from Hungary.
I still get the same blank page with the error posted before here.
So bad
Mine temporarily stopped working again but now has started again. Might be worth checking again.
Working now for me! Using a mastercard from UniCredit at hunguray!
Yes they finally did it 
I was happilly able to make topup from UniCredit Czech Republic
App version 7.30.2
First Direct have switched my current account to Mastercard from Visa. Now I can’t top up Revolut - it keeps saying wrong zip/postal code. i have checked and double checked the postcode both in my bank account and the app, (like I don’t know my own postcode…) I’ve tried leaving a space between and no space between the first four postcode digits. Nothing works. I don’t have another debit card.