A short while ago I had the hosting company of one of my clients add a SSL certificate to their website (www.mirjam-ouwerkerk.nl). Since then the webhooks fail to complete. The return status code is zero and when I hover over the status code the little hover text says "unable to verify the first certificate".
The reason I am reaching out to you first is that no browser has problems with the certificate (even on old Android 7 hardware) and also the payment provider we use has no problems calling webhooks to update payment information.
The payment provider does not connect with Prismic webhooks but is a separate service with its own webhook which it has no trouble calling.
The reason I mention browsers not having troubles and our payment provider not having issues is to illustrate that it probably is not a certificate configuration issue.