Paypal has very strict rules and strong customer protection. The agents are afraid if they let you use Paypal to pay for reps directly, that their account might get frozen. So you can't buy the items in your cart with Paypal.
So they have you top up your balance instead. Then Paypal just sees that transaction and it's nothing they're going to have a problem with.
This goes for all agents that don't require family and friends payments (all major agents), and even those who do might have a similar system put in place.
added: 9/28/2023 , modified: 9/28/2023