I've watched the Nick True video that came highly recommended in a bunch of Reddit results (e.g. here), but I still don't understand what's going on.
- Have all funds assigned, so that "Ready To Assign" is at zero.
- Approve a(n automatically imported) transfer from my checking account to my credit card account (see screenshot). Note that it is registered as an inter-account Payment and not as a regular expense.
- Budget view shows an equivalent amount of money "Ready To Assign".
After you have the money in Ready To Assign, did you have an overspent credit card category in the budget? If I try to replicate what you did, I do indeed have the money in Ready to Assign but I also have an overspent credit card category, and the fix would be to assign the RTA money to that credit card because you sent more to the credit card than you had set aside for the payment. If that's the issue, see https://support.ynab.com/en_us/when-your-credit-card-payment-category-is-red-a-guide-SJDSr3Q1i
That said, I usually don't have to do this so perhaps the reason is that you had some credit card payments that weren't budgeted for (maybe you only started with YNAB recently?).