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When a request (aka. raven) is sent, payload must include a
raven_macwhich is a
sha256generated using a secret key. That secret is added to the store when FieldsRaven app is installed, in rare occasions the app fails to add the secret key, when that happens, the incoming payload won't have a valid
This might be because you created the metafiled in Shopify admin and added a validation to the filed, make sure the data you send from the storefront is valid according to the validation you created and make sure the metafield type matches the type sent by FieldsRaven.