That worked! I was able to add RelatedItems by extending the endpoint
Hello, I ran into the exact same issue and found this post.
I created a new endpoint named RelatedItems. I have created other endpoints this way and they have worked, but the dev team is reporting this one is not working. What is different about this one?
As an add on to my question above I also asked the dev team if they could use the web service on the Acumatica Related Items screen. That does not appear to work for them either.