There can be a number of causes to connection issues but the 99% of them are solved with the following simple solutions.
Make sure you have completed all the setup steps.
Make sure you have followed the 5 steps to setup your headset with SideQuest - https://sdq.st/setup. You may have to manually install your drivers, here is a detailed tutorial on how to do that - https://sdq.st/drivers.
Make sure developer mode is enabled in the Oculus App
When the headset receives a firmware update this can cause the developer mode switch in the Oculus App on your phone to be disabled. This is a quick and easy fix thankfully, you just need to re-enable the switch in the settings of the app. See https://sdq.st/setup for more info.
Try another cable, preferably USB2 NOT USB 3
SideQuest uses ADB for installing apps to your headset. ADB can unfortunately have issues with certain USB setups, particularly USB3 connections. Use a USB2 cable or port to force the connection to downgrade to USB2 for a more relaible option, or try using Wifi in SideQuest instead.
I'm getting ‘adb server version (40) doesn't match this client(41); killing...’ or similar error.
This means you may have another version of ADB installed on your PC that is conflicting with the version SideQuest uses. Try searching your hard drive for adb.exe and remove any that are not contained within SideQuest folders. Sometimes apps will add additional ADB environment settings to your PC, these should be removed also. In the windows search bar type PC > right click This PC and click Properties then click Advanced System Settings on the top left. Click Environment Variables on the bottom of the window that opens then check both of those white boxes for ANDROID_ADB_SERVER_PORT or any other entries that include ADB and delete them if you find any. Save and close those windows and restart SideQuest
Some antivirus programs have been known to cause problems with SideQuest, particularly by quarantining the ADB binary files. TO test this you need to either check the Quarantine or Vault or what ever name the antivirus gives its staging area where it holds files. If you see adb.exe in there then please remove or allow it to run. You may also need to disable you antivirus to verify if it is causing problems. If the antivirus has removed some ADB files you may need to Uninstall and then Reinstall SideQuest to restore them.
VPN software can also affect how SideQuest works, we have seen issues with some VPNs particularly NordVPN. Sometimes you need to actually uninstall the VPN software, disabling it is not enough.
NOX or Bluestacks can cause issues since they appear as normal android devices to SideQuest. This means they can cause errors when installing things or end up installing correctly but you wont see the app/game on your headset obviously. Make sure you have removed any android emulators if you are experiencing problems.
Manually Testing the ADB connection
If you're on a Mac computer then you can also click the wrench icon in the top right and click “open ADB folder” - then drag these commands into a terminal window
For windows use the commands in CMD which can be found by using your windows start tab (bottom left windows button) and searching CMD then right click CMD and click run as Administrator
Type cd %appdata%\SideQuest\platform-tools\ Click enter Then adb devices Click enter
You should see: List of devices attached Example1SOTGDHHSD93 device
If you see Example1SOTGDHHSD93 unauthorized put on your headset now you should see the message to allow usb debugging - click always allow.
If you see 1SOTGDHHSD93 offline Then type adb kill-server and then use the adb devices command again.
If you see Cannot connect to daemon Then open up task manager and kill the adb.exe process by clicking it, then hitting end task for windows, else try the commands - taskkill /f /im adb.exe