"Michael SWS",
With respect, I think you have misunderstood.
If Ryanair charges exactly the same to use a credit card as it does to use a debit card (with the exception of Electron), how can it be perceived as suspicious if payment by debit card is not accepted?
The original poster made no mention of initially trying to use an Electron debit card.
I use my Electron card to book Ryanair flights frequently and have never experienced a problem.