I have followed below steps:
1) Upgrade the old firmware of router with RUT9_R_00.07.00
2) Added Wireguard package from package manager
3) Configured Wireguard interface only enter Private Key, keep port same 51820, ip address (not generated public key)
4) Added wireguard peer added key and allowed ip addresses.
5) Save and apply wireguard settings, it shows tunnel on page, turn on tunnel everything worked fine
6) Tried steps 3 to 5 again only changes are wireguard interface key and wireguard peer key. The problem started with connections.
7) I have tried restart router, add another instance of wireguard nothing worked
8) Upgraded the router firmware from server RUT9_R_00.07.002. not sure if it finished successfully, after reboot, I can see wireguard package was installed but could not see wireguard page under VPN so I have uninstalled wireguard package and repeated steps 2 to 5 but it does not show added tunnel on wireguard page.
9) Factory reset the router and upgrade the firmware from file to RUT9_R_00.07.00. same result as step 8
I can not upgrade the firmware to old version, when I browse the file it says file image is not correct. Can you please email me correct file for old version please?
I will send you troubleshoot file by email