Store App - customer email not sent

Hi Balbooa,
I've created a simple store, selling one item. Initially, the payment method is "manual" so I can test the system. The email notifications are again simple, please see image. I configured the default emails by updating their content, their status from New-> Completed, and deleting a couple of the unnecessary emails.

My test:
- create a new order
- manually move order status to "completed".
At this point, I always get the admin email, but I've never received the client email.

Checks so far:
- Confirmed the Joomla email works, by asking Joomla to send a test email
- The admin email always works, which supports the email system is working
- On the client notification email, I have changed the "from email" several times, using the admin email and several gmail accounts, to check the problem is not with a single email address
- I've checked the spam folder on the "customer email" address

Are there any other tests, or logs I can view, to check if an customer email is actually being sent out?

Would there be a problem the way my system is configured, I.e., a manual payment, and manually updating the status, with the client notification email set to "completed"?

Many thanks

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