Redis [QUESTION]

Hello, I have a question in my program. In my program, I use Lua, run command setbit to set Key, and use command get to read this key
This is my Lua script :

redis.call('setbit', KEYS[1], KEYS[2], 1);
local result = redis.call('get', KEYS[1]);
return result;

KEYS[1] is my bitKey. KEYS[2] is my bitKey index.

when I running my program, I get an error "ERR 'EVAL' command keys must in same slot".

I want to know why this error happened?