Maybe specific to the Ruby app, but to register dot.style webhooks like customer.tags_added you need to use both the ENUM_STYLE to register it and the dot style so the webhook handler knows where to send it!
{ topic: 'CUSTOMER_TAGS_ADDED', address: 'webhooks/shopify_customer_tags_webhook' },
{ topic: 'CUSTOMER_TAGS_REMOVED', address: 'webhooks/shopify_customer_tags_webhook' },
{ topic: 'customer.tags_added', address: 'webhooks/shopify_customer_tags_webhook' },
{ topic: 'customer.tags_removed', address: 'webhooks/shopify_customer_tags_webhook' }