Barclays Online Banking International Payment Error Code 33355

So I was just trying to make an international payment using Barclays online banking but it showed an error

We are experiencing technical difficulties and cannot complete this transfer. Please ring us on XXXX and quote us Code 33355

Luckily @jonboyes on Twitter had already had this problem and complained in 2017. Looks like Barclays haven't fixed the problem.

https://twitter.com/jonboyes/status/915197444211736577

The solution is to NOT paste the long numbers into the web page, but to manually type them in. Once I cleared the fields and retyped them the problem went away.