Your product data has been successfully added, but the stock is still empty? or do you have a purchase invoice that needs to be inputted in DealPOS? You can fill the stock by inputting Purchase Transactions / Purchase Order on the Buy menu, so that the stock of the products you just buy will be added to the Inventory. For a more detailed explanation, you can read this article:
Step 1. Go to Buy Menu
Buy Menu means you buy/receive products from the supplier.

You can choose an outlet that will stock the products that you input on the buy menu and enter the inventory outlet. The date and invoice number will be input automatically but you can also change it if you have the roles to do it. You can also input suppliers and pictures.
Step 2. Input Product - Pay
For example, I just added Chino Pants (28):

Step 3. Payment
There are options for direct payment or debt. If you choose directly there are several payment methods that you can choose. Click Ok to process the purchase.

Step 4. Purchase Complete

Step 5. Check Stock At Products or Inventory
Check stock at product detail.

Check stock at the inventory:

Purchasing Inventory from your Supplier Tutorial Video
You might also like to read this article:
If you want to make a Purchase Return, you can read the article here: Purchase Return
For COGS calculation in DealPOS, we have several calculation methods, including Average, LastOrder, and Manual. To set up, the COGS Calculation, go check this article: Setting Up Product's COGS Calculation.
If your store/business is selling electronic products such as smartphones, cameras, etc. that have a serial code or unique code for each unit, you can check this article for How to input the purchase: Purchase Order for Serialized Inventory.