EMV readers need to be "initialized " with the proper AIDs, CAPKs and Terminal settings to work. Together these 3 things make up what we call an EMV Configuration Profile. Profiles will differ depending upon many factors. This like what card brands will be supported. What Terminal Setting are desired (e.g. Unattended vs Attended). What country is targeted for deployment.
We (ID TECH's support team) are often asked what should my be configuration profile be set to. Understand, that the profile needed will be flushed out from the tests that must be passed to receive an EMV L3 certification
When one completes an EMV L3 certification with an app, a terminal and a backend processor, the AIDs CAPks and Terminal settings will need to be discovered. The backend processor will need to Identify the targeted card brands that will be supported. For each brand, there will be a suite of tests that one must pass. Each test will specify the needed AIDs, CAPKs and terminal settings needed to pass the test.
If you are using some sort of solution that is already L3 certified (like a virtual terminal type solution), then the provider will need to share with you what specific reader to use and provide a specific configuration profile.