This instruction should be used when a Client Card already exists in your Portal. See here if you need more information on what a Client Card is: What is a Client Card?
You can send the existing Client the link via email, SMS text or social messaging. This is only for a Client to book, not an Advisor, as the Cleint will be sent a confirmation. To send the link, you will easily add your Client's ID to https://gmg.me/pages/client/lets-chat/ so for example, the Client Card shown in the image below has an ID of 418626.
This means that the page to book their card is https://gmg.me/pages/client/lets-chat/418626.
This page will recognize the existing Client Card and the calendar opens to select a date and time of the Client's choosing.
