I've already posted about this in Welsh but here's the English version.

I am still having problems with websites refusing to accept my .wales email as valid.

In the past week it has been rejected by both AJ Bell and the Financial Ombudsman Service.

Why? .wales has been a valid Top Level Domain for over ten years now.

https://www.bbc.co.uk/news/uk-wales-29418898

#AJBell
#FinancialOmbudsmanService

New .wales and .cymru domain web addresses go live

Web addresses ending with .wales and .cymru are going live online after years of campaigns for a Welsh internet domain.

BBC News
@ApAlun I also experienced this a while back but can't remember where. I think it was a refusal to accept my email address because it was a .Cymru domain
@ApAlun I've once been told my .UK email address is invalid, which really shocked me.
@ApAlun AustraliaPost don’t recognise dot solutions as a TLD they can email invoices to but they do manage to send emails saying letters are in the box. Tells me everything I need to know about their IT systems.