Why can't I send a manual message?
This is because of the 24 hour limit Meta uses.
In the conversation view, you can see the conversations with your guests.
These conversations can be started by the property (through the initiated messages from the Guest Journey Builder), or by the guest.
Once the guest has sent a message (out of nowhere, or as a reply to an initiated message), the AI will reply and a conversation is started. Whenever there are messages going back and forth, Meta/Whatsapp will see this conversation as "active". As long as the conversation is "active", you can also step in and send manual messages.
24 hours after the latest received message of the guest, Meta/Whatsapp will see the conversation as "inactive". And that also means that you can not add a manual message anymore.
The conversation can only be reopened/activated again by a question from the guest or a reply to an initiated message.