searchRecords by a lookup field

searchRecords by a lookup field

Hello.
I'm trying to search a record by a lookup field, but it does not seems to work.
Here is the code line that doesn't works :
response = zoho.crm.searchRecords("Contacts","Premier_propri_taire :equals:" + EmploID"
Where "Premier_propri_taire" is a lookup field linked to a custom module and "EmploID" is the record of the Employee i'm trying to search.
Here is the message i get :

{"code":"INVALID_QUERY","details":{"reason":"the field is not available for search","api_name":"Premier_propri_taire "},"message":"invalid query formed","status":"error"}

I tried to search by Employee.get("id") but it seems I cannot enter Premier_propri_taire.get("id") as a searching parameter.

Here is the full code

response=zoho.crm.getRecords("Employ_s",1,1);
EmploList = list();
EmploIDs = response.toJsonList();
for each rec in response
{
EmploID = rec;
info EmploID;
EmploList.add(EmploID);
criteria = "Premier_propri_taire :equals:" + EmploID ;
info "crit"+criteria;
response = zoho.crm.searchRecords("Contacts", criteria);
info "2" + response;
}


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Thank  you for your help