ttysnoop.bt does not run properly

[gtataranni]

When run as bpftrace ttysnoop.bt pts2 it returns

$1 used numerically, but given "pts2". Try using str($1).

I have tried to look into str($1 + 3) with printf("arg+3 is %s\n", str($1 + 3)); with an exit right after. I wasn't able unfortunately to get my argument string as expected, or the argument from the 3rd char on, I would only get arg+3 is .
Interestingly, the BCC counterpart works