That field shouldn’t be required unless you have Require Accounting enabled for the location that you are logged into (or its location type, if it’s inheriting supported activities).
So the first thing to do would be to check the Supported Activities of the Location Type used for the current location. If Require Accounting is there, just remove it. If you’ve overridden the supported activities on the current location, then you’ll need to remove Require Accounting activity there instead.
If you want to use the Accounting features (which will be documented in more detail soon, I promise), then you can keep the feature enabled, but you’ll just need to add a GL Account to all products (or I believe they are inherited from their category if one is not assigned to the product).
So for example, go to product CIL50 to see if it has a GL account. If not just create a “default” GL Account and assign it to this product. Then go back to the PO and create that line item again. Let me know if that works.
FWIW, we have been feverishly adding accounting features so there might be some growing pains with the PO feature over the next few months. But we’ll add some tutorials and documentation once we finish the new Invoice and Centralized Purchasing features.