How to assign UID to struct value

How do we assign UID value to struct data.

I have a user with uid - “0x4” and I am trying to assign the user with the post using below construct but, it is not saving OwnerUserID data and it is storing everything :-

p := Post{
	CreatedAt:   &cdate,
...
	OwnerUserID: "<0x4>",
...
}

I have below post struct -

type Post struct {
	UID              string `json:"uid,omitempty"`
...
	OwnerUserID      string `json:"uid,omitempty"`
...
}

I have a schema of uid type for OwnerUserID, after running and fetching above code, I get below data -

{"me":[{"uid":"0x19","Title":"What should I do to improve my memory?","Tags":" life problem memory"}]}

So, you can see, it is not storing data of OwnerUserID

<!- hidden-now -> ~ due to sensitive data.

Solved with the help of @Clery