I have setup a payment portal that will allow contractor's to convert their account credits balance to money (Cashout) and transfer into their accounts on Paypal. What I have in mind is to set the buyer's email dynamically to the contractor's Paypal Email and run the Express checkout. However, does Paypal allow money transfer from a Business account (Seller) to a Person account (Buyer) using Express checkout? I'll appreciate any help on this.
Yes, you can do that no problem. Express Checkout includes parallel payments now, but you can actually set that up with a single receiver and you can set whatever receiver you want without messing with permissions or anything like that.
You'll use the PAYMENTREQUEST_n_SELLERPAYPALACCOUNTID parameter to handle it, where n refers to the individual payment in your request, starting with 0.
For a single payment being made, all the parameters like that would just be PAYMENTREQUEST_0_SELLERPAYPALACCOUNTID, but if you ever have an additional payment to somebody else you'd use PAYMENTREQUEST_1_SELLERPAYPALACCOUNTID, etc.
The documentation describes this parameter as:
Unique identifier for the merchant. For parallel payments, this field is required and must contain the Payer Id or the email address of the merchant. You can specify up to 10 payments, where n is a digit between 0 and 9, inclusive.