Richard,
the key you have to use is the package KEY not the package ID. You are confusing the package id (e.g. 4767) with the package key (e.g. payflowpro or authorize-gateway).
After you have setup the payment contract and an implementation --in your case payflowpro-- you go to the ecommerce package and enter 'payflowpro' as the PaymentGateway.
/Bart