If you are trying to install Planapple's "Save to My Trip" button in the Google Chrome web browser, and you are getting the error message "Download is not a CRX", this appears to be a problem that Google introduced in Chrome recently. It affects installation of any Chrome extension (not just Planapple's Save Button).
We're hoping that Google will fix this soon. In the meantime, here are three possible solutions that some people have had success with:
1. Quit Chrome, then restart it, go to Planapple, and try to install the Save Button again.
2. If that doesn't work, try installing in Chrome's "incognito mode": Press Ctrl+Shift+N to open an "incognito" window, go to Planapple (you'll need to sign in again), and try to install the Save Button again.
3. If that still doesn't work, try (re-)linking Chrome to your Google account: Go to Chrome's settings, choose "Disconnect your Google Account" (if it's connected), and then choose "Connect your Google Account" and link a Google account to Chrome. Then go back to Planapple and try installing the Save Button again.
(You can find more information on this Chrome issue by searching Google for "Download is not a CRX". The Google Chrome team has a bug report open on the issue.)