Freemius EDD Migration Helper in case EDD License keys have a custom prefix and are over 32 chars.

edd.php

<?php

/* 
....
Within plugin EDD Migration Client edd.php 
*/

/**
 * You should use your own unique CLASS name, and be sure to replace it
 * throughout this file. For example, if your product's name is "Awesome Product"
 * then you can rename it to "Awesome_Product_EDD_License_Key".
 */
class Awesome_Product_EDD_License_Key extends FS_Client_License_Abstract_v1 {

	// Previous key prefix
	protected $old_key_prefix = 'old-license-prefix-';

	// Previous license option key
	protected $old_license_option = 'local-license-key-option-name';

    function __construct()
    {
        my_freemius()->add_filter( 'license_key',  array($this, 'license_key_filter' ));
        my_freemius()->add_filter( 'license_key_maxlength', array($this, 'license_key_maxlength' ));
    }

    function license_key_filter( $license_key ) {

        if ( false !== strpos( $license_key, $this->old_key_prefix ) ) {
            $license_key = substr( $license_key, -32 );
        }

        return trim($license_key);
    }

    function license_key_maxlength( $maxlength ) {
        // The max length of your previous keys.
        return 32 + strlen($this->old_key_prefix);
    }

    /**
     * @author   Vova Feldman (@svovaf)
     * @since    1.0.3
     *
     * @param int|null $blog_id
     *
     * @return string
     */
    function get( $blog_id = null ) {
        
        $new_license_key = '';

        // Get local license
        $old_license_key = get_site_option( $this->old_license_option, '' );
      
        // If local key found and still over 32 chars
        if(!empty($old_license_key) && is_string($old_license_key) && strlen($old_license_key) > 32) {
            
            // We need to strip the prefix and make it 32 chars on the EDD store
            
            // Apply filter and get new key without old prefix, valid 32 chars
            $new_license_key = my_freemius()->apply_filters('license_key', $old_license_key);
            
            // Update the key on the EDD Store by sending both old / new key. 
            $response = wp_remote_post('https://your-edd-store.com',
                array(
                    'body' => array(
                        'prefix_edd_update_license' => array(
                            'old' => $old_license_key,
                            'new' => $new_license_key
                        )
                    )
                )
            );

            if ( !is_wp_error( $response ) ) {

                $response = wp_remote_retrieve_body( $response );
                $result = !empty($response) ? json_decode($response) : null;
                
                // If the update succeeded, save the new key locally
                if(!empty($result->success)) {
                    $this->set( $new_license_key );
                }
            }
        }

        return $new_license_key;
    }

    /**
     * @author   Vova Feldman (@svovaf)
     * @since    1.0.3
     *
     * @param string   $license_key
     * @param int|null $blog_id
     *
     * @return bool True if successfully updated.
     */
    function set( $license_key, $blog_id = null ) {
        return update_site_option( $this->old_license_option, $license_key );
    }

    // ....... //
}

functions.php

<?php

/* 
....
Within theme functions.php 
*/

function prefix_edd_update_license() {
	
	global $wpdb;
	
	$data = $_POST['prefix_edd_update_license'];
	$old = $data['old']; // OLD KEY
	$new = $data['new']; // NEW KEY

	// Find license by using old key, if found, update the key with the new one.
	$success = $wpdb->update('wp_edd_licenses', array('license_key' => $new), array('license_key'=>$old));
	
	// If license was not found using the old key, maybe it was already replaced by the new key, find it using the new key instead.
	if(!$success) {
		$found = $wpdb->get_var( $wpdb->prepare("SELECT license_key FROM {$wpdb->prefix}edd_licenses WHERE license_key = %s", $new) );
		$success = !empty($found);
	}
	
	echo json_encode(array('success' => $success));
	die();
}

if(!empty($_POST['prefix_edd_update_license'])) {
	add_action('init', 'prefix_edd_update_license');
}