What kind of license do you use for git repos for marketplace assets

Normally I use something like the MIT license when I put something on github.

But we’re interested in selling some code on the marketplace and hosting the code in a private git repo. If people purchase the plugin on the market place and ask to have access to the private git repo we would give it to them.

It seems like the MIT license isn’t the right license to use in this case since we would ideally want it to be accessible if people buy the marketplace asset, not just be open source.