Like the Google Play connection, this is what lets AppNatively submit your finished iOS build directly to App Store Connect, instead of you handling that step manually.
Steps
1. Go to Connect Google Play / App Store
Open Settings → Connect Google Play / App Store, App Store side.
2. Enter your Key Identifier and Issuer Identifier
Both come from your App Store Connect account.
3. Upload your ASC API Key
A key file (in the .p8 format) also generated from App Store Connect.
4. Save, then verify
Save your changes, then click Verify Connection and confirm the badge shows “Connected.”