Applying payments by Invoice functionality

Hello everyone, we are currently trying to set up SF Cashiering. Our objective is to use the apply payments by invoice, but we can't seem to make it work.

In our latest test we have done the following:

1. Access the post student payments component choosing and ID that we know has an unpaid invoice (the bill was generated using the "Identify student charges" component).
2. Then, select a target key configured with the "Applying payments by Invoice" .
3. Select the invoice in the prompt
4. We type the target value, select the tender and type the tender value (we are using a tender key with the type "cash")