Organization of the system of payment / payments

Question

Payment systems

Let's say there is an intermediary service, some kind of freelance. At the same time, mediation is carried out in the same way in financial terms:

1. The participant-customer pays from the real service to the service (replenishes his account) and places an order for work.
2. The participant performer performs the work.
3. Funds (almost) from the customer's account are transferred to the contractor's account.
4. The contractor withdraws funds in real.

Actually, the problem is how to competently organize the financial part so that the service is not used as a currency converter (let’s say I opened 2 accounts, offered a job with one, paid for Webmoney, the second accepted the job, “sort of did it”, received money to the account and withdrew, say, to map).
As I understand it, if you bother with this on your own (have your own separate input-output channels), then on each of your accounts you need (for insurance) to have funds sufficient for withdrawal by all participants. This is somewhat difficult and disadvantageous. You can shift all responsibility to some aggregator - all funds will come to his account and, using his internal rate and mechanism, be withdrawn through the appropriate channels. But here the problem may arise that the aggregator will not have or will not work with one of the payment methods, and their percentage is much higher than directly, and all the eggs are in one ...

What are the standard ways to organize such a scheme?

Answer 1

If the service takes its percentage for organizing the process, then "that's nice."
Well, as you yourself wrote ... either use the financial capabilities of third-party systems, or keep XXXXXX money on each type of payment system