How to lose customers through bad UX

I just got a strange validation bug, trying to buy something on eBay UK:

After about eight attempts (trying different browsers, local/international phone number prefixes etc), I emailed them to report it, and find out maybe if I am doing something wrong. Here is their response:

Hello Richard. My name is Elma from PayPal customer service.

I reviewed your account carefully to check why you are unable to use your card and saw that you were trying to pay a £555.00 GBP transaction with your credit card. It appears that this particular payment cannot be funded by a credit card because of our security model.

I would like to assure you that there is nothing wrong with your credit card or your PayPal account. As part of our commitment to protect you and all our customers, we review all transactions that go through us. This payment got declined because we detected that it might not be safe for you to use your credit card for this transaction. Don’t worry. I assure you that it’s just for this particular transaction. You can still use your credit card for your future transactions.

This is amazing. PayPal are reporting a permanent, this-form-will-never-work-so-don’t-bother-filling-it-out problem to users as an input validation error. And how do users react to validation errors? They double check their details and type them in again. And again. And again, until they’ve gone slightly mad, spending hours scrutinizing every pixel in every digit in their credit card and telephone number for mistakes.

In the end, it wasn’t until I contacted PayPal directly (hint: their feedback form is not exactly easy to find) that I was told my credit card would never work for this particular purchase, and the whole thing was a waste of time. (I wonder how many customers they lost who didn’t bother to fill out a bug report?)

If you are writing software like this, you have BIG problems.