The web page version of this email needs a URL. Learn more.
This error might appear if you've enabled a "web page version" of your email but haven't entered a URL. To fix this issue, please give the web page version of your email an actual URL or replace the empty slug. The error may persist if you've previously customized the plain text version of the email, and you may need to update references to the web page version of the email in the plain text email.