If the Current Stock of an item is a negative number and the additional stock added is not larger than the negative amount, the POS stock will still read as 0. Eg. the current stock is -88 and you add 69 units to your POS account, the new stock level increases to -19, however this is still a sub zero amount, therefore remains as Current Stock: 0.
Solution - Add enough stock to re-zero this amount and then + your actual stock amount to this number.
Example - Your current stock is - 88 and therefore it is showing as 0 on the POS Inventory. Let’s pretend the actual stock should be listed as 10. Therefore, you need to add 98 units of additional stock because -88 + 98 = 10.