The 24-hour WhatsApp window doesn't decide this. The usergroup permission Can re-open resolved tickets and its time limit decide whether a returning message reopens the old ticket or creates a new one.
How it works
Inside the time limit: the message reopens the resolved ticket.
Outside the time limit: a new ticket is created and the old one stays resolved.
Usergroup can't reopen resolved tickets: a new ticket is always created.
The time limit defaults to Forever. So by default, a returning user always goes back to their previous ticket.
Create a new ticket instead
Go to Admin > CRM > Usergroups and change the Everyone and Registered usergroups. Under Permissions, do one of the following:
Set a time limit: choose a limit for Can re-open resolved tickets, for example One Day. The limit counts days from when the ticket was resolved.
Turn off reopening: turn off Can re-open resolved tickets. Every new message after a ticket is resolved then creates a new ticket.
💡 Note: There's no separate setting for each channel. The permission and its time limit apply to WhatsApp, email, and the portal in the same way. The shortest limit is One Day.