WPvivid Backup for MainWP extension provides the ability to install and activate WPvivid Image Optimization Pro for your child sites from your MainWP dashboard.
Activate WPvivid Pro License
On your MainWP Dashboard > Extensions > WPvivid Backup for MainWP > on the Login page, enter your father license(you can found and manage your licenses on My Account area > License at wpvivid.com), click Login.
Install WPvivid Image Optimization Pro
Once logged in, you will be redirected to the extension dashboard.
On the dashboard, Choose Install & Claim WPvivid Backup Pro 2.0 from the dropdown menu, then choose Install WPvivid ImgOptim Pro Addon (beta) and select the child sites where you wish to install the plugin.
After that, click Apply button to start the process.
Once done, click the Sync Dashboard with Child Sites button on the dashboard, then on the child sites, you will see the WPvivid Image Optimization Pro Addon (beta) has been added successfully.