When applying 3 Payments as default payment and use a 100% coupons problem, must insert card number.

Hola

When I create a coupon of 100% discount to invite some Beta testers and I have selected 3 payments as default in a course, the platform doesn't let you continue in the process until you include you Card number. Even if you have nothing to pay due to the 100% discount. 

This looks like a bug, since it shouldn't ask for a credit card number. Any idea how to solve this? 

I temporarily solved by selecting the 1 payment option, but want to have the monthly instalment visible at the beginning.

Thanks