If you want your clients to Opt-in to text before you begin your conversations, you can enable the Double Opt-in feature in your account to send automated opt-in messages.
This is an organization wide feature that will apply to your entire team's settings and every contact will have to opt-in before you can start texting.
Opting In & Opting Out
1. Before you begin a conversation with a contact, you'll first send an automated confirmation text.
2. After your contact opts in, you can start composing your message.
3. If your contact responds "stop" they will automatically be opted-out and you won't be able to send texts to the contact until they opt-in again.
To enable or disable this feature, navigate to settings> organization settings > double Opt-in