If you see this error message, please check if
1. the email/sms content for missing } or overusing {{{
2. the custom values are valid:
3. the email addresses are valid:
e.g. test@gmail,com with a comma as the dot
Related article: https://help.gohighlevel.com/support/solutions/articles/48001155003-send-email-trigger-action-not-firing