Bug: email w/ attachment test email error

I drafted an email to All Members w/ an attachment. When I clicked the button to Send Test Email, I got the following message:

chezie.app says

Sorry, we ran into a temporary bug and can't complete your request. We'll fix it as soon as we can; please try again in a bit.

I tried drafting a new message later and the button for test email was still stuck as "Sending...." and wouldn't allow me to do anything else.