Is it possible to establish a relation between an item fulfillment and an invoice? In other words, If I have a Sales order with multiple item fulfillments and multiple invoices, is it possible to know what invoice corresponds to what item fulfillment? Maybe there is no relation at all...

There's no direct relation; they're both created from the Sales Order. I've had to do Invoice -> Sales Order -> Item Fulfillment in the past. Not super difficult in SuiteAnalytics, and I've seen scripts in the past that do that back and forward jump. I don't have anything current to share, unfortunately.

@Mark C, no problem at all. Basically same thing I said:

I believe there is an

orderline

field on both the fulfillment and invoice that could be used to establish some sort of relationship. However if a line was fulfilled and invoiced in two parts with the same quantity there wouldn't be a way of knowing exactly which invoice was created from which fulfillment. You should be able to use a custom field and script to store your own link

Yeah, It's an odd request indeed. Custom fields + script(s) should somehow do it. Thank you.