How to Add TLDs Purchased in WHMCS :
With your WHMCS software, you can resell the domains again, but this needs to link your WHMCS to the registrar you are a seller of. Then you'll have the option to assign the various top-level domain (TLD) extensions you want to sell, first check the registrar domains such as .com, .net, and .org. Do not add other extensions such as PRO
Steps to add domain extensions to your shopping list:
Step 1: At first you are logged in to your WHMCS
Step 2: Go to the Setup tab, click Top Products / Services, and then choose Domain Pricing
Step 3: Add TLD extensions through the bottom row of the list.
Step 4: In this box, specify the additional services you provide.
Step 5: Set the automatic recording option for the extension
Step 6: Click the Save Changes icon.