Basically once verify by the credit card processor, a token will be created (token is an encrypted and compliant with Banking rules).
Token is what we used to communicate securely with the cc processor and clearance house. The app is just a facilitator and no more no less, the rest is taken care by the credit card processor/clearance house. Therefore, we do not store and credit card info or data. It is then just passing through via token.
All credit card processor and Tokenization work the same way.
Therefore, you can feel secure about that.