WHMCS : CURL Error: 7 - couldn't connect to host

Setup > General settings > Security > API IP Access Restriction

I added both the IP's to the list. The main IP for the reseller account 10.10.10.10 was to be added onto the API list.

http://docs.whmcs.com/ResellerClub#CURL_Error:_7_-_couldn.27t_connect_to_host

However, this did not fix the issue.

The second fix was to check the settings for the server.

Setup > Products & Services > Servers > "Select the server" and click on edit settings button

Check whether all the settings are entered correctly and also check the settings for Secure access.

Check "Enable ssl mode for all connections"

This fixed the issue.