Why when i make purchase order for a certain product inventory does not increase ?

Hi there, @animalyardpharma.

Let me share with you some insights on what transactions affects your inventory in QuickBooks Online (QBO). 

Non-posting transactions such as purchase orders and estimates don't affect your quantity on hand. This is the reason why your inventory doesn't increase when creating P.O. 

Once you convert it to a bill ,cheque, or expense, then this will now add value to your stocks. Here's how:

1. Select + New and choose Expense, Cheque, or Bill. 
2. From the Payee ▼ drop-down list, select the supplier. This opens a window with their open purchase orders.
3. Click Add for the correct purchase order. This adds the items from the purchase order. They appear in the Item details section.
4. If you plan to bill a customer for a specific item, select the Billable checkbox. Then add the customer you plan to bill in the Customer column.
5. Click Save and close.

For additional reference on when to use expense or bills, check out this article: Learn the difference between bills, cheques, and expenses in QuickBooks Online.

Sometimes you might discover that you have either more or fewer of an item than QuickBooks shows. If you track inventory in QBO Plus, you can manually adjust an item's quantity without recording a purchase or sale.

Let me know if you need further assistance with this. I'm always around to provide answers and clarifications to your questions. Have a great day ahead and take care!