Please try the following steps based on your device.
Situation 1: PC
Disable any active VPN/Proxy. Ensure you have a stable internet connection. Try switching to a different network, such as from Wi-Fi to a Wired or mobile hotspot.
Situation 2: Mobile
Verify that the country or region set in your payment method matches your current location. Ensure you downloaded the game from the app store that corresponds to your region. If the game is from a different region's store, you may need to reinstall it from the correct one.
If the issue continues, try restarting the game after changing your network before attempting the purchase again.