Add new contact but didn't add to member list

{
"email_address": {
"address": "[email protected]",
"permission_to_send":"explicit"
},
"first_name":"test test",
"create_source": "Contact",
"list_membership":["36835928-ec85-11ec-b253-xxxxxxxxxxxx"]
}

I got this response :

{
"contact_id": "c2833c6e-ecb1-11ec-bab9-xxxxxxxxxxxx",
"email_address": {
"address": "[email protected]",
"permission_to_send": "explicit",
"created_at": "2022-06-15T13:47:55Z",
"updated_at": "2022-06-15T13:47:55Z",
"opt_in_source": "Contact",
"opt_in_date": "2022-06-15T13:47:55+00:00",
"confirm_status": "off"
},
"first_name": "test test",
"create_source": "Contact",
"created_at": "2022-06-15T13:47:55Z",
"updated_at": "2022-06-15T13:47:55Z"
}

I have two. questions:

First  "confirm_status": "off"  why confirm status off ?

Second the contact didn't add to my list