Payment marked as processed, yet no activity on buyer nor seller side

[JeroenA]

I created a smart button. All seems to work fine.

Yet, I was contacted by a buyer claiming he paid using the smart button.

We spent an hour, making payments. Everything went through well, payment made, statement shown, notification given to the system.

Yet, again when checking our accounts, no money was transferred.

In my back office I can see the transactions, all marked as successful.

My buyer is located in GB, I'm in the Netherlands.

Any thoughts, advise?