Custom Freemius Opt-in/out Code Snippet.

freemius-opt-in-out.php

<?php
// $choice contains the user's input to opt-in or out.
if ( 'yes' === $choice ) {
	if ( ! is_multisite() ) {
		my_freemius()->opt_in(); // Opt in.
	} else {
		// Get all sites on the WP multisite network.
		$sites      = Freemius::get_sites();
		$sites_data = array();

		if ( ! empty( $sites ) ) {
			foreach ( $sites as $site ) {
				$sites_data[] = my_freemius()->get_site_info( $site ); // Get site info from Freemius.
			}
		}
		my_freemius()->opt_in( false, false, false, false, false, false, false, false, $sites_data ); // Opt-in with all sites data.
	}
} elseif ( 'no' === $choice ) {
	if ( ! is_multisite() ) {
		my_freemius()->skip_connection(); // Opt out.
	} else {
		my_freemius()->skip_connection( null, true ); // Opt out for all websites on multisite.
	}
}