Hi  @Javier Guardo  , this looks like bug, thanks for reporting this. In this case, does the prospect you are testing the email have an email address? I noticed I was able to reproduce this if I was emailing a prospect without an email address (or by deleting the "To" in the main email editor).

If you make sure the email is set above in the "To", the test will should work as expected (and it will go to the correct test email, the form is just throwing an error that the "To" email address is missing, even though it will not be used here).