My client also tested some things and if you want to register as a Producent on update.act4you.nl/producenten/inschrijven-als-producent.html with a coupon code you end in this error;

I don't understand what this has to do with your original issue. In the future if you've multiple issues simply make multiple topics. Mixing issues in 1 topic just creates confusion.

As for the error it states exactly what your issue is with "Amount negative". You're trying to charge a negative amount, which isn't possible. Ensure your coupon can't cause a negative amount by using a percentage based coupon. Only use static value coupons where you know it can safely apply to the plan (condition it so it can't apply to plans that would cause this situation).

I already send a PM on the original post and included this issue to.

I never received a PM from you. Are you sure you sent it to the correct person? See my signature for a link to directly PM me. Check the sent tab in your private messages and delete the message if sent to the wrong person.

The strange thing is that we are using the 100% discount code and it works for models but not for producers.

I'm guessing Models and Producers are your CBSubs plans? What payment gateway are you using? A 100% free plan shouldn't send to the gateway at all and become instantly activated.

Have reviewed your install. You're using a payment gateway we did not develop (Sisow). Contact the developer of your gateway as the error is in the payment gateway it self. Note Stripe supports iDeal payments and we did develop the Stripe gateway that is included with CBSubs so you may want to consider changing payment processors.

As for the fields not mapping it's because you're applying a condition against them that logically makes no sense to registration. You've your address fields set to make sure the profile owner has the Registered usergroup. This can't be valid during registration so their values get reset and there's nothing to map. Edit your address fields then under Integrations > CB Conditional remove the conditions or at least expand Locations and toggle the condition off for registration and profile edit as I suspect you wanted this to apply to profile view only.