Send the verification link only from the same WhatsApp number that you've provided above.
Type of group join
Direct Link : Users can join directly by using the group link.
Direct Chat : A user sends a WhatsApp message to the admin. When a user clicks on the "Join Group" button, WhatsApp is opened and with the admin number automatically. So a user can chat directly with an admin of a WhatsApp group. After that, the admin can decide whether to join him in the group or not.
Admin Confirm : The admin sends a WhatsApp message to the user. When a user clicks on the "Join Group" button, a notification is sent to the group admin on his profile page or notification page in Joinmygroups. The admin accepts the user there by clicking on the user's details, and then the group joining link is sent from the admin to the user through WhatsApp. In this case, the admin must periodically visit the notification or profile page of Joinmygroups to check if any user has requested to join.
Form Submit : Users must fill out the form to join the WhatsApp group. The form can be customised by the admin.
Joinmygroups
Join WhatsApp groups