When your mail merge stopped, and YAMM tells you that the service has been invoked too many times, it is usually because of personalized attachments and quota limits. Please read this article to learn more.
Why do I get this error?
If you get a notification of the following error:
It usually happens when you are including personalized attachments to your emails, and have exceeded the quota for that day.
Indeed, due to restrictions from Google side, the sending limit drops to 100 emails / 24 hours when you have attachments in your emails, and if you are using a Gmail account. This limit also applies when you are under a paid plan (and therefore, you won't be able to send more than 100 emails / day). Consult this article (end of the page) for more details about your daily quota with attachments.