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:
http://PortalServer:1507/devtest/api/sv/vse/service/mar/VSE/http?securityToken=l7qg22rj2g05a11doe89l0la6k6tana4
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:
http://PortalServer:1507/devtest/api/login
In the request body we would need to have the username and password like the below sample:
{"username":"admin","password":"admin"}
The response will contain the accessToken in the response body:
"access_token": "9ikf0m83p8oagf7g3nb89f6bq7mqtp1q",
With this information you will be able to send the GET request:
http://PortalServer:1507/devtest/api/sv/vse/service/mar/VSE/http?securityToken=9ikf0m83p8oagf7g3nb89f6bq7mqtp1q
Make sure to update the PortalServer address, the VSM name and the securityToken.