Hi @dougaitken we have also got a client where this manifested in the exact same way – and I can confirm that removing the webhook signing secret in WooCommerce settings and saving allowed to send the webhook from Stripe.
Literally doing only those two actions, in quick succession
1) Remove signing secret and save in plugin’s WooCommerce settings; and then in another tab
2) At Stripe, in Webhooks, find a recently failed attempt and click “resend”
This was successful.
Note, we have many clients using Stripe where none of this applies. There’s two on the same setup where this is happening. Trying to find the root cause. Note we can assist with a debug on this @dougaitken – hit me on WC Slack or we can raise or add to a GitHub ticket. Posting here in case anyone has this issue in mean time and wants to quick fix.