I am using a DJI Mini 3 Pro with the DJI RC-N1 controller. Currently I am running with:
Aircraft Firmware: 01.00.0500
RC Firmware: 04.14.0400
Fly App version: 1.6.9(1005-official)

I am using a Samsung S9 (Android v.10) phone as I have been ever since I bought the Mini 3 Pro. A few days ago it automatically upgraded the aircarft firmware and yesterday it prompted me that there was a new version of the Fly App. When I accepted the offer to update, the process fails with "App not installed" message and reverts back to 1.6.9. Tried the process by manually downloading and installing the latest versions (1.9.8 and 1.9.9) with the same outcome. The  "About" box in the Fly app is still showing v1.6.9(1005-official) and the "Check for Updates" shows  V1.9.9 with a red dot next to it whatever that is.
I desperately want to use the Gain and Expo features on my drone but are unable to. Any suggestions? Please help!

Hi there. Thanks for reaching out, and we're sorry for the inconvenience. Here are some recommended troubleshooting steps you need to try:
1. Go to the mobile phone’s System Settings>Apps and find “Installing an Unknown Application.” Enable the “Allow application installation from this source” switch.
2. Check the mobile phone’s internal storage, and clear its cache. The remaining memory must be greater than 2GB.
3. If the “Installing an Unknown Application” setting has been enabled already, please back up the photos and videos. Uninstall the earlier version of the app and then restart the mobile phone. Download and install the app from the DJI official website again.
4. If the DJI Fly app cannot be installed from the browser, try to find the APK file of the DJI Fly in the File Manager for installation. (Alternatively, re-download the installation package, and move it to the device’s internal storage root directly for installation.)
5. Check whether the network/device has the permissions for the DJI app (some networks or systems have no permissions for the DJI app, and the DJI app may not be installed, and some customized devices have not obtained the permissions for the DJI app).
Please keep us updated. Thank you.

DJI Tony Posted at 3-31 23:38
Hi there. Thanks for reaching out, and we're sorry for the inconvenience. Here are some recommended troubleshooting steps you need to try:
1. Go to the mobile phone’s System Settings>Apps and find “Installing an Unknown Application.” Enable the “Allow application installation from this source” switch.
2. Check the mobile phone’s internal storage, and clear its cache. The remaining memory must be greater than 2GB.

I have an S9, cleared the cache and it updated fine.

If you're still haven't problems. A workaround would be to download the app via the website and then install it.
https://www.dji.com/downloads/djiapp/dji-fly

I updated my triple tek 8 pro via my profile, setting firmware update with the drone off.

djiuser_KxXL8dpy8dsj Posted at 4-1 00:23
I have an S9, cleared the cache and it updated fine.

Hi there. Thanks for letting us know. Please reach us back should you have other concerns or inquiries. Have a nice day!

MS Posted at 4-1 01:14
If you're still haven't problems. A workaround would be to download the app via the website and then install it.
https://www.dji.com/downloads/djiapp/dji-fly

Thanks. As I said in my original message, I have tried that manually already and it still failed.

Hi all. It's finally working. I followed your tips (clearing the cache and retrying from the profile) and it worked. This time it prompted me to confirm that I was happy to have an application from an unknown source, install its software on my phone (which is what DJI Tony suggested). v1.9.9 is know installed on my S9 and I am very happy indeed! THANK YOU!

Alexis Images Posted at 4-2 13:03
Hi all. It's finally working. I followed your tips (clearing the cache and retrying from the profile) and it worked. This time it prompted me to confirm that I was happy to have an application from an unknown source, install its software on my phone (which is what DJI Tony suggested). v1.9.9 is know installed on my S9 and I am very happy indeed! THANK YOU!

We're pleased to know it worked and that you managed to install the latest app version on your device. Should you have other concerns, please reach us back here at DJI Forum. Thank you.