No emails being sent – help please

Apologies if I am being thick, but…

On my test site, I use the plugin Stop Emails to stop them actually being sent and the plugin Log emails which lets me view what would have been sent.
This all works fine and emails for bookings or changes to booking are logged as expected. The sending method is WP Mail.

I have an event with one booking pending. I have configured Events Manager – Email Users leaving the sending method as Sendmail. I go to my edit event page. It shows 1 pending booking – as expected. I click on Send Email and – nothing happens – no email logged. I have tried disabling the Stop Emails plugin but still nothing received or logged.

Hav I got the wrong end of the stick here?