Perhaps you have tested a specific version of the Sales Igniter rental system and only want to release that to your production server. We only stored the latest version of the modules on our composer repo, but here is a way to handle this case.
Request from us the version that you need if you don’t already have it.
Make a folder if it doesn’t already exist at vendor/salesigniter/packages and within that folder put the module zip file
Run this in command line replacing /path/to/magento with your full magento root folder path:
composer config repositories.salesigniterartifacts artifact /path/to/magento/vendor/salesigniter/packages
In the below command replace 1.1.202108016 with the specific version you want to use
composer require salesigniter/releaserental2:1.1.20210816