How do I troubleshoot a transactional email not being sent?

Transactional emails have three parts:

1. Campaign Monitor email template
2. Smart email mappings in Salesforce
3. Salesforce Flow

We'd first suggest testing the transactional email itself (parts 1 & 2) and our code that triggers the send from Campaign Monitor. This removes the Salesforce flow from the equation and specifically focuses on the transactional email.

You can test that via the Salesforce transactional email template. On the email mappings table, next to the mapping, click the dropdown, and then Run Test. You will be prompted to enter a Salesforce Id from a test record (ensuring it matches the root object you are working with). 

Once the code has been executed, the email can take up to 10 minutes to receive. If the email has not been sent, please contact us for further help. Please also note that your Campaign Monitor account must be able to send transactional emails. If you have any questions on this point, please contact Campaign Monitor directly.