After you start a conversation, your client or potential client has the opportunity to reply to that conversation, then you can reply to them.
When a client responds to your conversation, you will receive a notification in your PhotoBiz account. The easiest way to reply to a conversation is to do so through your notifications.
To begin, click on the bell notification icon, then click on the email address of the conversation you'd like to reply to. You'll see the conversation so far, and at the bottom, a text box to enter your reply. Enter your reply here and click on send.