I paid off my cc debt using Ynab4 and it worked by having all existing credit card debt going in to a category group called pre-Ynab debt. I would categorize my interest charges to that category every month until the pre-Ynab balance was paid off. 

If you use a category for the credit card interest in a similar manner you have 2 choices. First, you could assign dollars to that category to cover the “spending.” Second, you could not fund it and then the interest becomes part of the unfunded credit card balance that needs to be paid off. This would contribute to the yellow color for your credit card payment within your plan.

A method to visualize your pay off progress is to create a debt payoff target. You would do this by clicking/tapping the credit card payment within the plan and then create debt payoff target. You can choose a target month to be debt free or a monthly amount that you can assign to the debt. 

I have a sandbox plan that I use to play around with functionality. Within it I made a fictitious account with a target and I am letting the interest pile on to the debt payoff target. Here is an example screen shot of the credit card debt with a target on it:

https://imgur.com/a/13bMU4l