I can't get the predicate argument

[Raphael (Raphaël Derbier)]

We actually support uid() in both SUBJECT and OBJECT.
So the mutation is working.
The issue is in your query:

@djmastov

{
    users(func: type(User), first: 10) {
        uuid
        updated_at
        HAS_CONTACT @facets
		}
}

HAS_CONTACT is a relationship so you must query something from the related node to get a result
Just add
HAS_CONTACT @facets { uid }
as a result, you should get something like

{
            "uid": "0xd",
            "HAS_CONTACT|created_at": 1732640718
}

Let me know if that works.

BTW you can simplify the query to get the uids:

contact_query_{idx}(func: eq(phone, "{contact_user["phone"]}")) {{
                    contact_{idx} as uid
                }}

is equivalent to

contact_{idx}  as var (func: eq(phone, "{contact_user["phone"]}"))