1. Switch it on and set the rules
Configuración → Pagos diferidos holds the institution's switch and the rules every plan follows: the allowed terms (say 3, 6 and 12 months), the minimum amount to defer, whether a saved card is required and whether the first installment is charged today or next month.
You can limit which concepts may be deferred; with none ticked, every concept is eligible.
The portal has its own switch and its own concept: the one used when a client schedules an amount with no underlying charges. Turn it on last, once the rules are the way you want them.