For WhatsApp, the message is undeliverable due to the recipient being an invalid user on WhatsApp.
For WhatsApp, reasons can include:
Recipient phone number is not a WhatsApp phone number.
Recipient is using an old, unsupported version of the WhatsApp client for their phone.
Confirm with the recipient that they have accepted Meta's latest Terms of Service for WhatsApp. If they have not, then send them this link
to accept the latest WhatsApp Terms of Service.
Confirm with the recipient that they have an active WhatsApp phone number on the latest client version for their phone.