Welcome to the community @Gracie
You get this message when there's an invalid variable in your email. It'll be surrounded by curly brackets {} in the email content or it may be in the display logic if you're using that. Are you able to share the email content here and also what event you are previewing eg, checkout started, order placed etc
Regards
Andy
Hey Gracie!
Like Andy said, this is almost always due to a curly bracket being in the wrong place or even just being duplicated - like {{{event.product.title}} - because I have three brackets on the left, I’d get a variable error on my entire email.
If this is a dynamic email, cross-check all of your variables to confirm!