It seems you are facing issues purchasing data through your MTN app. Here’s a step-by-step guide to help resolve this problem:

1. Check Network Connection:
- Ensure that your device is connected to a stable Internet connection. Switch between Wi-Fi and mobile data to see if it makes a difference.

2. Update the MTN App:
- Navigate to the App Store on your iPhone.
- Search for the MTN app, and check if there is an update available. If so, tap "Update" to install the latest version.

3. Restart Your Device:
- Restarting your iPhone can resolve temporary glitches. Hold down the power button and slide to power off. Wait for a few seconds, then turn it back on.

4. Check for Account Issues:
- Log in to your MTN account on the app. Ensure that your account is in good standing and that you do not have any pending payments or account issues that may hinder data purchases.

5. Re-verify Payment Method:
- Within the MTN app, go to your account settings and re-add or verify your method of payment. Ensure your payment details are correct and up to date.

6. Contact Customer Support:
- If the problem persists, reach out to MTN customer support for assistance. You can usually find the contact details within the app under "Help" or "Support".

7. Check Device Compatibility:
- Confirm that your device is compatible with the MTN service you are trying to access.

If you follow these steps and the issue remains unresolved, contacting MTN directly is your best option for specific troubleshooting related to your account and the app functionality.