This was Sam's solution:
Your 'headers' you are sending are malformed.
The 'add header' VI adds a key/value pair to the HTTP header. You are building the key value pairs yourself instead of letting the VI do them for you. You should call the 'add header' VI for each key/value header pair you want to send.
To do the authorisation, you just need to put 'Authorization' into the 'header' control and then your 'Basic **password**' as the value. That will add a line "Authorization: Basic **password" to the headers. The HTTP Client VI handles the other headers automatically itself (e.g. the timestamp).
You should check what is actually being received by the server (e.g. by checking server logs / logging the request / using a 3rd party checking service etc.).
