Go to Setup > Products/Services > Domain Pricing. Delete all TLD price and re-do the process. In most case changing template fixes the WHMCS domain checker issue. You can do one of the following ways and check.

Navigate to Configuration ( ) > System Settings > Addon Modules or, prior to WHMCS 8.0, Setup > Addon Modules. How to fix WHMCS Domain Checker not Working.

The addon will now appear under the Addons option in the top menu.

Some addons will also have additional options specific to the addon module.

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Click Configure and select which administrator roles you wish to have access to the addon by enabling them under the Access Control section. 1 billing and management software for cPanel powered web hosts.

The addon is now active within your WHMCS.

Click Activate next to the addon you wish to enable.

Navigate to Configuration ( ) > System Settings > Addon Modules or, prior to WHMCS 8.0, Setup > Addon Modules, and the addon you have uploaded will be listed.

In cPanel, when you create an addon domain name, a subdomain is added automatically for it, as well as an FTP user that has access to the document root folder of the addon domain.

Subdomain or FTP Username - this field is automatically populated when you input the new addon domain name, but you can change it if you want. Once uploaded the addon will be available within your admin area. New Domain Name - the addon domain name, i.e. Unzip and upload the addon files to the /modules/addons directory within your installation location.

To install a new addon to WHMCS it will first need to be uploaded to your WHMCS installation.

Cpanel shortcuts domains_addons whmcs