So on my end I would need a system to accept the transmission accept the activation? So it would go something
Register -> payment processor -> my data base? with a yes or no on activation.
Register -> payment processor -> my data base? with a yes or no on activation.
You'd have to talk to the payment processors and see what their communication protocols require.
I suspect there is a lot more validation in the communications then that, but at the most basic level, that's probably correct.
Keep in mind that the payment processor needs to be very sure that they are actually communicating with you and not an imposter. There will probably be some form of encryption and digital signatures used in the communications. They will probably have required specifications for the data that is passed back and forth. Activation may include a message indicating how much value to load into the account. Account numbers may be required to have a particular number of digits, and those digits may have checksums, issuer identification values, and parity bits that allow the processor to verify that the number was read correctly by the POS and determine which issuer to send the messages to. The card processor may also include information such as a merchant ID so you can track where the card was activated.
but Pos companys do not like people to know how it works for security reasons I imagine. 
