The SH1 has a switch that toggles between external CV/Gate and the Keyboard:
Does the keyboard work when the switch is set to “Ext”, but nothing is plugged into the sockets?
if yes, then assumingly your external Gate signal is too weak. It must have 10 Volts. A 5 Volt gate like from many eurorack devices will not work.
If no, then assumingly the contact of this switch that feeds the Gate signal is correded.