Item search by custom field

I have only one deal with custom field = “xxxxx” .I’m trying to get this deal.
I’m trying to use the /itemSearch/field endpoint, but what i’m getting is the 404 HTTP response.
This is the URL i’m using:
I’m making something wrong or this response means that there is no Deal with the ‘‘xxxxx’’ custom field?

Here’s a wiki page that could help with the challenge

Let me know if you still face any challenges.