App Store on iPhone does not accept my billing address on Visa. I want to buy ChirpOmatic, but it insists that my billing address has to be in a USA state. I live in France!

Is your country and region and billing address set for your current location and are you using a credit card from a local bank?

All Apps are not available in all countries.

1. Open the Settings app. 
2. Tap your name, then tap Media & Purchases.
3. Tap View Account. You might be asked to sign in.
4. Tap Country/Region.
5. Tap Change Country or Region.
6. Tap your new country or region, then review the Terms & Conditions.
7. Tap Agree in the upper-right corner, then tap Agree again to confirm.
8. Select a payment method and enter your new payment information and billing address, then tap Next. You must enter a valid payment method for your new country or region.* Learn more about how to change or remove your Apple ID payment information. 

Because you are logged in to the US App Store.