Hello! I understand you're having trouble adding an existing booking to your KLM app on your iPhone running iOS 18.7. Let's work through this together to get your booking added.

First, could you tell me a bit more about the issue? For example:

- Are you entering the booking reference and your last name exactly as on your ticket?
- Did you book the flight directly through KLM or through a third party?
- Do you have a Flying Blue account linked, or are you trying to add it without logging in?
- Are you getting any error messages when trying to add the booking?

Meanwhile, here are some initial steps you can try:

1. Verify Booking Details: Double-check your booking reference code and last name for any typos.

2. Update the App: Make sure your KLM app is fully updated to the latest version available in the App Store.

3. Log Out and Log Back In: Sometimes logging out of the app and back in can refresh your data.

4. Add Booking Without Account: Try adding the booking by selecting “Add Booking” and entering just your booking code and last name without logging in.

5. Check Network: Ensure your internet connection is stable—try switching between Wi-Fi and cellular data.

If these don't help, let me know if you see a specific error like “booking not found.” Some users experience this when flights are booked through partners or codeshare flights, which might cause syncing issues with the app.

Also, if your booking is very recent, sometimes there is a delay before it appears in the system accessible by the app.

Should these steps not solve it, we can dig deeper into your account settings or possibly check if there is a temporary server issue.

Could you please share the details when you attempt adding the booking and what exactly happens? This will help me guide you better.

Are you satisfied so far with the assistance?