I\'m building an application where a user can connect their own Paypal account through Paypal Permissions SDK (https://github.com/paypal/permissions-sdk-ruby). I was able to
When calling API on behalf of other account, you need to add parameter "subject" to indicate the account that you are calling API for. The value of "subject" could be the account primary email address or payerID. Then the money will go to the account which was the value of subject.
Yihui gave the right answer. But I wanted to explain/post here what I did to fix my problem (using Yihui's guidance).
You need to get the Payer ID from the 3rd Party Permissions SDK of Paypal. So you will need to ask for the following "ACCESS_BASIC_PERSONAL_DATA", "EXPRESS_CHECKOUT", and "REFUND".
Then you will need to use the NVP (Name Value Pair) SDK of paypal to perform Express Checkout on behalf of another party/merchant.
For more information, we followed the following article of Paypal https://developer.paypal.com/docs/classic/express-checkout/ht_ec-singleItemPayment-curl-etc/