NAP stands for National Advantage Program. You may get a discount if you use a NAP doctor. However, a discount cannot be guaranteed under the NAP for any particular claim.
But... and it's important:

NAP doctors are NOT in-network for your plan.

That means you are likely to pay more for a NAP doctor than an Aetna in-network doctor. To pay less, use a doctor in the Aetna network. Please note that Aetna relies on third parties to report changes in provider participation in the NAP. So NAP provider information is updated much less frequently than is the case with Aetna networks. Always check with a NAP provider to confirm that they are current NAP program participants.