The API call to download a MAR file is available starting with DevTest on release 10.3.
I you are using a previs release you can try the following GET call can to download a MAR file:
Where PortalServer is the address where the Portal service is running, http is my VSM name and the securityToken value is the accessToken generated when we login to the Portal.
The following POST call can be used to generate the securityToken/accessToken:
In the request body we would need to have the username and password like the below sample:
The response will contain the accessToken in the response body:
With this information you will be able to send the GET request:
Make sure to update the PortalServer address, the VSM name and the securityToken.