How to pass request through HTTP " GET " statement - vba

Question

I'm trying to fetch data from a currency api. I'm fairly new to VBA and very new to JSON, but I can't figure out how to pass a request through the HTTP.... I can fetch any data I want that does not require a request though to pin it down.
The API is here: https://www.bitfinex.com/pages/api
I'm trying to pass a timestamp(time) request. See instructions ( pasted form their website just below )
Trades
GET /trades/:symbol
Get a list of the most recent trades for the given symbol.
Request
timestamp (time): Optional. Only show trades at or after this timestamp.
limit_trades (int): Optional. Limit the number of trades returned. Must be >= 1. Default is 50.
Response
An array of dictionaries:
tid (integer)
timestamp (time)
price (price)
amount (decimal)
exchange (string)
type (string) "sell" or "buy" (can be "" if undetermined)
My code so far
Private Function get_price() As String
Dim xml_a As Object
Set xml_a = CreateObject("MSXML2.XMLHTTP")
With xml_a
.Open "Get", "https://api.bitfinex.com/v1/trades/BTCUSD", False
'' <<< something should be written here right? I just don't know what... >>>''
.send
get_price = .responseText
End With
Set xml_a = Nothing
End Function
Sub tester()
Dim JSON_return As Object
Set JSON_return = JSON.parse(get_price())
Debug.Print JSON_return.Item("last_price")
End Sub