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.
Here's how it works
1. Before you begin a conversation with a contact, you'll first send an automated confirmation text.
2. After your contact replies "Y" you will see your text board to start composing your message.
3. If your contact responds "stop" they will automatically be opted-out and you won't be able to continue the conversation until you send the confirmation text again and they reply "Y".
You can enable this feature in Settings > Organization Settings > Double Opt-in