Update an Existing or create New Relationship based upon custom field value

I would like to be able to set a relationship between two different custom posts types based upon a value stored as a custom field in one of the post types. this stored value is the same value as the post id of an existing post that i wish to relate it to.

In this case, I have 'equipment' and 'clients' that require relating. I will set the correct 'client' post-id in a custom field registered to 'equipment' that is named 'wpcf_related_client_post_id_via_select_field'. When i then update/save the 'equipment' cpt i wish to have the relationship set between the two cpts.

i have a few different use cases for this, firstly to be able to use it as a 'work around' to set the relationship via a csv wp-allimport uplaod, and secondly so that i may be able to create relationships to other custom post types based upon their already existing relationships to the one being updated/created.

ie, i have ttwo other cpts 'job-sheets' and 'engineer-reports' that relate to 'clients' and 'equipments'. My hope is by using this kind of method I will be able to form relationships between all relevant cpts as they are generated in turn.

ie - 'clients', 'equipments', 'job-sheets' and 'engineer-reports' can all relate to one another in various ways and I would like to have the relationships programatically set.

<?php 

add_action( 'rwmb_equipment-details-admin_after_save_post', 'update_client_equipment_relationship_from_client_post_id' );

function update_client_equipment_relationship_from_client_post_id ( $post_id){

	//get id from related client post id via text field
	$related_client_id_value = rwmb_meta( 'wpcf_related_client_post_id_via_select_field', $post_id );
	                            
        MB_Relationships_API::add( $related_client_id_value , $post_id , 'clients-and-equipment-relationship'  );
}

I have tried the above code but i does not seem to create the relationship. please can you share any pointers in the right direction?