When I run the node.JS code below I get a header value of

Try the same values for keys and nonce in your code and compare

var nonce      = 1516453770998;
var API_KEY    = 'PUBLIC KEY'
var API_SECRET = 'PRIVATE KEY';

var md5 = crypto.createHash('md5').update( JSON.stringify( {'Currency'
+:"PAC"} ) ).digest();
var requestContentBase64String = md5.toString('base64');
var signature = API_KEY + "POST" + encodeURIComponent( 'https://www.cr
+yptopia.co.nz/api/GetBalance' ).toLowerCase() + nonce + requestConten
+tBase64String;
var hmacsignature = crypto.createHmac('sha256', new Buffer( API_SECRET
+, "base64" ) ).update( signature ).digest().toString('base64');
var header_value = "amx " + API_KEY + ":" + hmacsignature + ":" + nonc
+e;
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