Currently in Vero, to receive and display stats on a campaign that has been sent using a Mailgun provider, the Mailgun API key you provide to Vero must be the same as the Webhook Signing Key. If the keys have been cycled in Mailgun or are not the same for any reason, you must ask one of our support team members to add the webhook signing key manually. A better solution would be to add a 'Webhook Signing Key' field in the providers UI so that users of Vero can add the key themselves when setting up.