Can I use Flex for payments from a virtual card linked to a pot?

I made a purchase over £30 from a virtual card which was paid from a pot. I assumed I could then charge this to Flex, but the button is not appearing. Is it not possible to charge payments to virtual cards to flex? Or it is because the payment is from a pot?

You can’t Flex after the fact if you used a virtual card from a pot to make the transaction in the first place.

Thanks, that seems like an odd restriction. Do you know why they decided not to allow that?