Option Explicit
Public Sub GetClosePrices()
    Dim lastRow As Long, url As String, ws As Worksheet, tickers(), dateString As String

    Set ws = ThisWorkbook.Worksheets("Sheet1")
    With ws
        dateString = Format$(.Range("A1").Value, "yyyy-mm-dd")
        lastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
        If lastRow >= 3 Then
           .Range("K3:K" & lastRow).ClearContents
            tickers = Application.Transpose(.Range("A3:A" & lastRow).Value)
        Else
           Exit Sub
        End If
    End With

    Dim s As String, re As Object, p As String, r As String, prices(), i As Long
    ReDim prices(1 To UBound(tickers))

    p = """DATE_HERE"",""open"":([0-9.]+)"   'Format must be YYYY-MM-DD
    p = Replace$(p, "DATE_HERE", dateString)
    url = "https://cloud.iexapis.com/stable/stock/TICKER_HERE/chart/1m?token=pk_98e61bb72fd84b7d8b5f19c579fd0d9d"
    Set re = CreateObject("VBScript.RegExp")

    With CreateObject("MSXML2.XMLHTTP")
        For i = LBound(tickers) To UBound(tickers)
            .Open "GET", Replace$(url, "TICKER_HERE", tickers(i)), False
            .send
            If .Status = 200 Then
                s = .responseText
                r = GetValue(re, s, p)
            Else
                r = "Failed connection"
            End If
            prices(i) = r
        Next
    End With
    ws.Cells(3, "K").Resize(UBound(prices), 1) = Application.Transpose(prices)
End Sub

Public Function GetValue(ByVal re As Object, ByVal inputString As String, ByVal pattern As String) As String
    With re
        .Global = True
        .pattern = pattern
        If .test(inputString) Then  ' returns True if the regex pattern can be matched agaist the provided string
            GetValue = .Execute(inputString)(0).submatches(0)
        Else
            GetValue = "Not found"
        End If
    End With
End Function