You should save order number in message meta, that way is recommended.
If you want message id same as previous message id, you can update using https://github.com/shamim2883/front-end-pm version. Uninstall current version and download and install github version.
remember if your database copy is already updated you cannot use that database copy. Use database copy before update.
After update finish uninstall github version and install your latest PRO version of the plugin.

Let me know.

Please follow step by step
1. Use your database backup copy which you made before this plugin update. Messages once updated cannot be updated again. So make sure you are using backup copy of your database which backup you made before this plugin update to 10.1.1.

2. You can use github verion OR you can use current PRO version. If you use PRO version make sure to make these 2 changes https://github.com/shamim2883/front-end-pm/commit/2d0eec44b5824bd5526d0b9532d309771700a533 and https://github.com/shamim2883/front-end-pm/commit/ec6221f36e4d451140683380da9d1e547605c940

3. Now click “Proceed” in admin notice and continue update.

These 2 changes backported to current version. So if you update this plugin now, then no need any more file changes. Just click “Proceed” and continue.

Use

add_action( 'fep_display_after_message', function(){
	$authordata = get_userdata( fep_get_message_field( 'mgs_author' ) );
	
	if( in_array( 'business', $authordata->roles ) ){
		echo '<div id="businesslink">See more information and photos of <a href="' . esc_url( home_url( '/' ) ). $authordata->user_nicename . '">' . $authordata->display_name . '</a>.</div>';
	}
});