When using an undimensioned array is there a way to write the array to a file? Something like this

DIM C()
C('TEST') = 2
C('WEST') = 5
C('BEST') = 1
WRITE C on myfile, 1

I believe the I have followed the instructions to attach a document to the body of a post request but nothing is being sent out in the files{} port of the request.  I can either get the stream in "data", not visible at all, or visible but no form data. Any help would be appreciated, below is what I have:

ClassMethod SendFax(phone As %String, coverpath As %String, docpath As %String) As %String
{
     Set req = ##class(%Net.HttpRequest).%New()
    //test server
    Set req.Server = "httpbin.org"
    Set req.SSLConfiguration = "CardChoice"
    
    Do req.InsertFormData("Username",##class(HData.