The 'Welcome email' to Participants is NOT automatically sent at the time of adding a new participant. You can manually send them the welcome email from their Participant Details page.
This gives you control over when the email is sent, and is activated by 'Send Welcome Email' from the menu at the top right of their participant details page.
View the section titled Grant Planability Access on their profile to see their username and if and when the Welcome Email was last sent:
If a participant requires assistance to login, you can resend the Welcome Email which includes their Username and a link to login. They will need to create a new password by following the prompts.
You can also Update their Password for them.