Henk You can set limits in the whitelist entry for individual merchants. They will be taken into account for online payments at that specific merchant. You can also set global payment limits on your cards, those are valid for every payment.
If this is your first online payment at a new merchant, a whitelist entry will be generated for you. But this means, that you can't individually limit the payment, as the merchant is not known to bunq at that point. If you really want to, you could reduce your global limit until you have the whitelist entry to modify.
I hope that comment made sense and was not written too complicated.. π€