Greetings,

Thank you for contacting MWS support.

PFA the enumeration for the MTR reports
1.GST_MTR_B2C
2.GST_MTR_B2B

For more information please visit the below link
http://docs.developer.amazonservices.com/en_IN/reports/index.html

Thank you for highlighting it we will have it updated in the amazon portal.

Thank you,
MWS Support