Newsletter signups not receiving mail: status 400

Hi,

My client has the option to sign up for their newsletter and receive a 10% discount. Most of the time new signups are not receiving this email. This is the error message received:

{“status”:400,“response_body”:“{"message":"Cannot deliver an automation that is not valid"}”,“verb”:“POST”,“url”:“https://email.shopifyapps.com/flow/action”,“request_body”:“{"properties":{"delivery_target_id":"gid:\/\/shopify\/Customer\/5974932619511","marketing_activity_id":"gid:\/\/shopify\/MarketingActivity\/123279114427"},"shopify_domain":"olivi-lyn.myshopify.com","action_definition_id":"Shopify Email Automation Flow Action","shop_id":-1,"action_run_id":"1bd59b08a59f38a7a99623ad901ff1f0d6b5eb03"}”}

Any ideas what is going wrong?

I get this too… any idea anyone?