502 Bad Gateway - Trying to post invoices to MYOB

Third party posting into MYOB from CRM software getting "502 Bad Gateway Microsoft-Azure-Application-Gateway/v2" 

URL is  https://secure.myob.com/oauth2/account/authorize/?client_id=9evez3yqwew2jx3exgrhy2vz&redirect_uri=https://waterbrothers.myflo.com.au/myflomyob&scope=CompanyFile&response_type=code&state=[F3002BA13A9A49298DCFC1FEE4D51A76]

Is this an MYOB or our third party issue?