If you're unable to make the Enable Sync toggle "stick" under your account, that is it turns itself off when you go back to your account there might be a quick solution! :)
This is a very rare bug and not directly associated with ReadMe! but has to do with the internal keychain management in iOS.
Try turning the passcode off for the lock screen on your device (in the iOS settings). If sync doesn’t work after this, try turning the passcode on again and try sync again.