Cannot send messages as an agent when creating a Ticket or Request with custom "via"

Hello everyone.

I'm trying to create tickets through API (especially /api/v2/tickets.json) when my end users ask for it from a WhatsApp channel. This would be the request I do:

But notice that when changing the property "via.channel" from "api" to "whatsapp" the agent's chat in Zendesk Support website stops working correctly. It won't send messages when I click send or press Enter. Furthermore, the debug console throws the following error:

In fact, if the "via.channel" is different from "api" it simply won't work, not just the value "whatsapp". I have to change it because the property "from_messaging_channel" is always false if "via.channel" equals "api" and I need it to be true.

Every time I open the tickets created in Zendesk Support Chat as an agent, the following error appears:

I would really appreciate to know if these property are meant to be changed, if I'm doing something wrong or why no other channel is working.

Thanks!