We are planning to start an freelance service platform having global sellers. Can anyone suggest how to setup the payment flow structure?

There are a many ways to setup payment in online marketplace. Here are a few examples:

1. Use a credit card processing service - This is the most common way to handle payments, and it's easy to set up. You just need to sign up with a reputable company and enter your billing and shipping information.

2. Set up a gateway account - A gateway account is a type of payment account that allows you to take credit or debit card payments online. This is a good option if you want to accept payments from a large number of customers simultaneously.

3. Use PayPal - PayPal is one of the most popular payment methods online, and it's easy to set up. Just sign up for an account, add your business information, and start accepting payments.

Whatever payment method you choose, make sure to keep your billing and shipping information accurate so that customers have an easy time paying for your services. And last but not least, remember to keep your business running smoothly by keeping an eye on expenses and making necessary adjustments as needed!

You could opt for an escrow service wherein the money can stay for the duration the project is being completed by the freelancer and post completion gets transferred to the freelancer from the client
OR
You can block a certain amount from the client's wallet for the duration they are engaging a freelancer

Legislation varies across different countries. When you hold other people's money you become a custodian, in the early days of a startup you can do it without a license, but at some point you would probably have to become compliant. That's why for early stage startups I recommend using payment gateway providers like:
- PayPal Commerce Platform for platforms and marketplaces: https://www.paypal.com/en/business/platforms-and-marketplaces
- Stripe for marketplaces: https://stripe.com/en-es/use-cases/marketplaces
- MANGOPAY (only in Europe): https://www.mangopay.com/pricing/

All these providers count with licenses and compliance teams to ease you the task of having to deal with it on your own.

I'll be happy to share with you some examples of what I've done with my startups and with the companies I consult.