There should a page in our documentation that contains step by step instructions on how to install MMS Backup in this scenario specifically focusing on the fact that you need to download all the various releases of MongoDB that you plan to back up.

The Sys Admin install MongoDB was unaware of the following:
(1) he needed to manually download and an unpack all the required releases
(2) He didn't know where to download them from
(3) He didn't realize that there are two versions of MongoDB: community and enterprise and he needed to ask those questions to figure out what versions of MongoDB to download
(4) He wasn't clear about what the structure of the mongodb-releases directory should look like when he was done.

Some of the information is available here but you really have to know what to look for to find it.

I apologize if this page already exists, but I could not find it.