The relationships may be correct, but there are different types of relationships possible, one to one, one to many, many to one, many to many, and we'd need to know that before we can answer the question.
A one to one relationship would allow this to happen as simply if the two fields were in the same table. The same is true for many to one. But one to many and many to many can require pulling up a group of related records on a different layout in order to update the entire group.
Thanks for the reply Phil. I found my error. I had created via calculation a unique transaction number but neglected to make sure that all of the results were text. The resulting find requests were not a match therefore stopping my script. All is now well.