Syntax error in JISON with simple grammar

I’m trying to implement a very simple parser, but I’m having a problem. I have the following grammar:

axioma : '{' list_instr '}' EOF;

list_instr : list_instr instr
           | instr;

instr     :  call_func;

call_func : 'call' ID '(' params_list ')'
          |  'call' ID '(' ')';

params_list : params_list ',' NUM
            | NUM;

The grammar contains more productions but it is this part that is creating conflicts. The problem comes when trying to parse the following text:

{
    call add(2, 3)
}

JISON tells me that there was a syntactic error in ‘(‘, however the characters are provided by the lexical analyzer, so I think the problem may be the grammar but I really don’t understand what the cause is. Any ideas?