Try deleting all of your mods, delete forge from your versions folder and install forge again from the forge website. You still have the problem try redownloading vape from the website, and also check if your account information on the vape.gg website (Ip address, hwid) is up to date. Also if you are on a vpn you also can’t inject vape. Or if any of this is not working contact support at vape.gg/contact.
V3 only works for 1.7.10 and 1.8.9