I have the same problem; I am being paid in EUROs into my HSBC currency account and wanted to do REVOLUT to for better FX rate and as a day-2-day current account (while im in UK or traveling in EUROZONE)
I tried topping up the revolut account from my EURO account and the HSBC online banking and I was getting errors:
Invalid BIC number
I called the HSBC customer helpline and gave then the IBAN number (GB one) showed on the app and the HSBC representative said the IBAN numbre is invalid (checking it online has shown it is valid)
After another 10 minute wait and him checking stuff internally basically the issue was:
IBAN is valid however; Revolut ltd shows up as online bank based in UK however it is not registered as a member of Association of British Banks (or something along the lines) and as such it’s not on a whitelist and the IBAN code is not accepted.
REVOLUT - get your stuff together; looking at the forums you really struggle with regulatory framework/being a member of appropriate trade bodies in UK and as such the services don’t work well with UK based providers…