Hi there! I understand you're encountering an issue where a purchase in the MAC.BID app fails with a message saying it "cannot read document." Let's work through this together.

To start, could you please tell me a bit more? For example:
- When exactly does the error pop up (right after tapping purchase, during payment, or after)?
- Have you tried this purchase on a specific item or any item?
- Is your internet connection stable when this happens?
- Have you recently updated the MAC.BID app or your iPhone's iOS?

Meanwhile, here are some initial steps we can try to resolve the "cannot read document" purchase error:

1. Restart the MAC.BID app: Close the app completely (swipe it away from recent apps) and open it again. Sometimes this refreshes temporary files.

2. Check for app updates: Go to the App Store and make sure MAC.BID is updated to the latest version. Updates often fix bugs related to purchases.

3. Restart your iPhone: A quick reboot can clear temporary glitches.

4. Check your internet connection: Try switching between Wi-Fi and mobile data to see if one works better.

5. Clear app cache (if MAC.BID allows it): Some apps have a cache clear option in settings to remove corrupted files.

6. Reinstall the MAC.BID app: If nothing else works, uninstall and reinstall the app. This will clear any corrupted app data which might cause document read errors.

If you can also confirm your iOS version (you mentioned 18_6, which I assume is iOS 18.6), that's great. This should be compatible with the app.

Let me know what you've tried or if you want me to guide you through any of these steps!