Need to create a callback URL to get incoming SMS messages from API

Need to create a callback URL to get incoming SMS messages from API

Hi,

I need to get all incoming SMS notifications from a site I use for my application.

I created a callback on the site I use for this task. 
https://smsgateway.me/sms-api-documentation/callbacks

Can anyone help me how to accomplish this? I'm not a developer but I was able to create everything I need for my app by myself until I hit this stumbling block.

This post seems to answer my questions but I can't access the links. 
https://help.zoho.com/portal/en/community/topic/api-and-url-callbacks


Any help will be much appreciated.