I am coming back to you to give you an update about this issue!
We have been in contact with Sisigma (by email and phone). It seems like their payment provider needs to help them with a software update 🤗. We will contact their payment provider too, to make sure that this gets done 💪.
In the meantime, they have suggested that to pay with bunq, you can click on “Bank Transfer”, and then you should be able to make the payment using bunq, as a normal bank transfer 🤑
We will keep this issue updated as soon as we have any more news!