Most thumb throttles are cheap garbage, and looking at the Yose site looks like they are no exception. If you have a multimeter and some connectors, wire it up to a ~3V DC source like 2 AA cells wired in series. Check the voltage on the output. Since there are a bunch of variables, I'll leave it to you to find your exact details. Also check that both sides of the plug are in good condition. And finally, thumb throttles are pretty cheap to replace. Grin is my source for all things ebikes related: https://ebikes.ca/ebike-parts/control-stuff/throttles.html

One more thing to try, if you have cables going from the brakes try disconnecting them. Motors are usually setup to cut out as soon as the brakes are hit, so a switch jammed on might cause what you're seeing.

At what speed are you testing?

The primary function of an ebike throttle is to provide walk assist which never exceeds 6 kmph.

Some throttles provide boost during riding, but only while you are pedalling.

If you don't get any support while pedalling regardless, the issue is your sensor/controller/motor and not the throttle.