Mismatch data type expected data type BIGINT found dataType STRING

Mismatch data type expected data type BIGINT found dataType STRING

pl = zoho.crm.getRecords("CustomModule1",1,200);
info pl;
pl_pc = pl.get("Product Category");
info pl_pc;

I'm getting repeated errors of the type:

Mismatch data type for function at argument index __ expected dataType BIGINT found dataType STRING.

"Product Category" in the CustomModule1 is actually a picklist, so I don't understand why it is expecting a BIGINT type.

Can someone please help?

info pl;    returns the CustomModule1 items just fine.