Hi there! I understand you're getting a message that says you don't have a valid address in the MapQuest GPS Navigation app on your Mac. I'd love to help you sort this out.

Could you tell me a bit more about the address you’re entering? Is it a full street address with city and zip code? Also, is this happening with all addresses you try, or just one particular location? Knowing this will help me narrow down the cause.

In the meantime, here are some initial steps we can try:

1. Double-check the address format: Make sure you’re entering the full address including street number, street name, city, and postal code. Sometimes missing elements can trigger the invalid address error.
2. Try typing the address into MapQuest's online latitude and longitude tool (available on their help site) to verify if it recognizes the location. This can help confirm if the address itself is valid in MapQuest’s database.
3. Clear your browser cache and cookies if you are using MapQuest via a web browser on your Mac. Sometimes stored data can cause location recognition errors.
4. Ensure that your Mac’s location services are enabled:
- Go to System Preferences > Security & Privacy > Privacy tab
- Select Location Services and make sure it's turned on and that MapQuest (if listed) is allowed to use your location.
5. If you’re using an older version of the app or browser, try updating it to the latest version available, as outdated software can sometimes cause errors.

If after these you still get the invalid address error, it might be a mapping data issue. In that case, MapQuest recommends reporting the problem directly through their support page to get the location data corrected1.

Could you try these initial steps and let me know how it goes? If you can share the exact address or a screenshot (without personal info), that might help me assist you better as well.