Other Important Note From TaxPro GSP:
1. New eInvoice auth API v1.4 is now available in Sandbox http://gstsandbox.charteredinfo.com (as per Release Notes (einv-apisandbox.nic.in)
2. Start using https://einvapi.charteredinfo.com for EWB, eInvoice, and ASP Api at the earliest opportunity.
3. Please make sure you are passing Header "Content-Type" : "application/json" in ALL post requests.
4. No need to pass Accept: application/json header. Remove the Accept header if it’s adding escape chars (\) to response Json.
5. Old sandbox at http(s)://testapi.taxprogsp.co.in is deprecated and is mapped to http(s)://gstsandbox.charteredinfo.com as of now until it would be phased out in couple of months.
6. It's suggested that SAP users enable SNI so that they will not face TLS certificate issues... https://answers.sap.com/questions/599994/ssslerrservercertmismatch.html
Warm Regards,
TaxPro GSP Team.