I wanted to check in to see if you've been able to resolve the issue.
Have you tested the Webhook URL with different data? If that came through successfully, then I suspect that the App/API sending the data to the Webhook doesn't have the correct permissions to send that specific information over to Zapier.
You can use a tool like https://webhook.site/ to generate a Webhook URL and have the same App/API send the data to it, if it shows the same error, then the issue is from the App/API.
Cheers.
DANIEL -Zapier Support