Make the Easy Invites plugin compatible with Wordpress Multisite

General information for the website: Plugin enhancement
Description of every page/module: Wordpress plugin development
Description of requirements/features: please see above
Extra notes: Hello, I'd like to use this plugin here: https://wordpress.org/plugins/baw-invitation-codes/ on a wordpress multisite.
It currently only works on a Wordpress single installation. (it only needs to work in one site in the wordpress multisite)

My budget is up to £300, but I would like to come in below this.

Thanks.