The smart plug needs to be always “on” even when the light isn’t. Otherwise it wouldn’t be able be able to hear the next “on” command from the network. So if anyone turns it off with a dumb switch, it can’t come back on again until the current is restored. A common issue in smart home installations.
I’m not sure exactly which model you have, but most of the plug ins have a button on the front that you can push to manually turn on the controlled device. Not always conveniently placed though.
The other alternative is to provide a separate control button that’s nearby,conveniently placed, and obvious to visitors, etc. see the following topic for some examples:
The other alternative is to replace the load controlling switch with a smart switch, but that requires wiring.