Hi @21Rocks,
Let's get your purchase order saved and get rid of the error message.
On the Purchase Order page, other than the Item details section, there's also Category details. If you've entered information under the Category details section but left the Category column blank, then this is the source of the error message.
I suggest you go through the Category details section, and check each line item, making sure that each of them has a category selected.
I'll also leave these articles for your reference:
These two articles are step by step guides on how you can link an estimate to a purchase order, as well as how you can apply a purchase order to a vendor transaction, respectively.
Have other questions in mind? Place them below, and I'll be sure to take of them for you.
