The Subject is not typed wrong.  I would like to know if we can Link a Invoice to a Sales Order? There are times when we do Projects and items and Item Quantities tend to get Added / Deleted / Modified. This is very common.

For example, some item which was initially part of the order, is later on deleted.  Or, some items which were not part of the original order, gets added during the Project.  So, the best way to go about is Create the Sales order at the end of the project by converting the Invoice.

OR 

We can create a new Sales Order, and Zoho should allow us to link it with the free Invoice(s).  Else, the Sales Order will keep showing as Open.

Kindly Advise.

KB