Hey there ! Thank you OP @BenjaminButton for this detailed post. I am experiencing the same issue and I don't have the solution but I noticed something which could be interesting : I'm using the transaction trigger with 3 credit cards. 2 are VISA and trigger correctly. The 3rd card is Mastercard and gets the error everytime. As you mentionned you were using a "Cembra" card, I checked and found out that Cembra is using Mastercards as well, maybe this could explain the origin of the error. Hope this information could help to fix the issue.