No Activity in Merchant account

[Qenesis]

I have set up my sandbox accounts and am using the REST API with curl libraries in a C program.

I create an Order with intent: CAPTURE and user_action:PAY_NOW.

This succeeds and I receive an order ID.

I then paste the Approve URL into a browser, login as my sandbox user and pay.  My browser displays the results from PayPal accepting the payment.

Back to the C program, I then call https://api.sandbox.paypal.com/v2/checkout/orders//capture, which succeeds.

If I now login to my sandbox user account, there is a payment transaction for each time I have done this successfully.

However, if I login to my sandbox merchant account, there is no activity at all.

Is there something else I need to do to finish processing the payment ?

[locustv2]

Are you still able to do CAPTURE after paypal redirect back to your site?

After i click the PAY NOW on paypal and execute the CAPTURE, i am getting this: 

Request failed with code: 403, message: {"name":"NOT_AUTHORIZED","details":[{"issue":"PERMISSION_DENIED","description":"You do not have permission to access or perform operations on this resource."}],"message":"Authorization failed due to insufficient permissions.","debug_id":"3759af8ec147c","links":[{"href":"https://developer.paypal.com/docs/api/orders/v2/#error-PERMISSION_DENIED","rel":"information_link"}]}