tml_deactivate_extension_license()

function tml_deactivate_extension_license( $extension ) {
    $extension = tml_get_extension( $extension );
    if ( ! $extension ) {
        return false;
    }

    $response = tml_extension_api_call(
        $extension->get_store_url(),
        array(
            'edd_action' => 'deactivate_license',
            'license'    => $extension->get_license_key(),
            'item_id'    => $extension->get_item_id(),
        )
    );

    if ( empty( $response ) ) {
        return new WP_Error( 'http_error', __( 'An error occurred, please try again.', 'theme-my-login' ) );
    }

    if ( false === $response->success ) {
        return new WP_Error(
            'deactivation_failed',
            sprintf(
                /* translators: %1$s: URL to deactivate the license on thememylogin.com. */
                __( 'Unable to deactivate license. Please deactivate it on <a href="%1$s" target="_blank">our site</a>.', 'theme-my-login' ),
                'https://thememylogin.com/your-account/?action=license-keys'
            )
        );
    }

    return $response->license;
}

View src/includes/extensions.php, line 272 on GitHub