Can I give my sub agents a credit limit so they can book on my portal without paying upfront every time?

Yes, this is normally possible, and it is one of the main reasons agencies put their sub agents on their own portal instead of taking bookings over the phone. Each sub agent gets a login and a wallet or ledger of their own. You set how much they are allowed to spend, and every booking they make is taken off that balance. When the balance runs out they cannot book again until they top up or until you raise the limit, so you are never exposed further than the amount you agreed to.

You stay in control of the whole thing from your own admin. You can add money to a sub agent when they pay you, reduce or increase their limit as your relationship with them changes, and see a statement of what each one has booked and what they still owe. Some agencies give a generous limit to the sub agents they have worked with for years and keep newer ones on a prepaid balance until they have proved themselves, and you can mix the two freely.

There are a couple of things to be honest about. The credit is yours, not the supplier's, so if a sub agent does not pay you the loss sits with you and the software can only enforce the limit you set. Whether this feature is switched on, and how much detail you get in the statements, can depend on your plan, so it is worth confirming before you sign sub agents up.

If you plan to work this way, decide your starting limits and your top up process first, then ask for the sub agent module to be enabled and test it with one friendly agent before you open it to everyone.