All my customers are updated as Unregistered business and it still shows that invoice does not have valid information.

Now when I follow the suggestion and go to update fields, I get very contradictory things...My invoice items are listed as services with valid SAC code, but it says this:

In the screenshot the product type is shown as Goods and in Red, it says You have changed product type for this item after creating invoice. But nothing has been changed. The product type was setup before I actually started creating invoice and it was properly set as Service with SAC code.

There seems to be some serious issue with your backend or something sis screwed up. So kindly fixed these disparity ASAP.