I've only seen the Sinclair ZX81. If the ribbon cable is similar (and it sure looks similar from a cursory image search) you should be able to fix the keyboard

I've only seen the Sinclair ZX81. If the ribbon cable is similar (and it sure looks similar from a cursory image search) you should be able to fix the keyboard with just two electronics-related items, a multimeter with continuity mode and electrically conductive tape. On the ZX81, the metal on the ribbon cable is exposed on one side. Which means you can put one multimeter lead somewhere close to the bottom of each trace, and the other lead you trace along the exposed wire. If your multimeter stops showing continuity, you know you have a break there and if you look really hard you should be able to see it. If you have a lot of breaks close to the connector (quite likely), take a pair of scissors and cut off the part with the break and plug the remainder of the ribbon cable back in. Otherwise, cut the electrically conductive tape into a thin slice and tape that over the affected spot. (Soldering won't work, you'll just melt the ribbon cable).