I was on a Ryanair flight in early October from Luton to NOC which was delayed by over three hours (due to a maintenance issue, and Ryanair choosing to send an engineer over from Stansted rather than have a local contract at Luton).

I submitted my claim a couple of weeks later using https://complaint.resolver.co.uk/ which was recommended by a friend who had used it (and is also recommended by MoneySavingExpert). Complaint Resolver don't charge any fees - they just provide a channel for you to manage your claim (this is the first time I've ever used or even heard of them).

Ryanair immediately asked for my bank details, and paid it within 10 days of my claim.

Worth noting that the 250 euro compensation was paid in GBP (at a very reasonable exchange rate) - but Ryanair didn't actually tell me they would be paying it in GBP. Whilst this isn't surprising (considering the flight originated in the UK), I gave them a EUR bank account as I assumed it would be paid in EUR !