We receive the 131026 error from Meta for the following reasons.
When we are unable to deliver message. Reasons can include:
The recipient phone number is not a WhatsApp phone number.
Recipient has not accepted our new Terms of Service and Privacy Policy.
Recipient using an old WhatsApp version; must use the following WhatsApp version or greater:
Android: 2.21.15.15
SMBA: 2.21.15.15
iOS: 2.21.170.4
SMBI: 2.21.170.4
KaiOS: 2.2130.10
Web: 2.2132.6
Mitigation steps for the above error
Using a non-WhatsApp communication method, ask the WhatsApp user to:
Confirm that they can actually send a message to your WhatsApp business phone number.
Confirm that they have accepted our latest Terms of Service (Settings > Help, or Settings > Application information will prompt them to accept the latest terms/policies if they haven't done so already)
Update to the latest version of the WhatsApp client.