How do I message all my clients at once with bulk messaging?

You can bulk message clients by using a saved message template and sending it to a client list/audience.

Basic workflow:

Create or choose a message template
Use an Email or SMS template depending on how you want to reach clients.
Templates let you reuse the same message and include client-specific merge fields like their name.
Go to your contacts/clients list
Filter or select the clients you want to message.
This could be all clients, a specific list, past hunters, leads, etc.
Select multiple clients
Use the bulk select option if you want everyone in the filtered list.
Choose the bulk message/send action
Pick the template you want to send.
Review the message before sending.
Send
Confirm the recipients and send the bulk email or SMS.

I went ahead and opened Message Templates so you can start by creating or editing the message you want to send.

Pick or build a template in Message Templates, filter your Contacts list down to the audience you want, select them in bulk, choose the bulk send action, and confirm. The same template can merge in each client's name.