Your webhook signing secret doesn't look correct unless Stripe generates different formats for different accounts. It should be prefixed with whsec_ and not just we_.
Navigate to Developer > Webhooks then click your webhook URL. You should then see a "Reveal" link under "Signing secret". Click that then copy and paste the full signing secret to your Stripe gateway in CBSubs for the "Stripe webhook Signing Secret" parameter.
Their documentation also indicates it should be prefixed with whsec_.
stripe.com/docs/webhooks/signatures
We don't verify that it is so there's no limitation in our system if Stripe did change this, but it seams like the signing secret is incorrect and would be why the IPN failed.