By default, all free email domains (Gmail, Hotmail, Yahoo, etc.) are blocked from creating a free trial account.
In order to use your free email domain, your email address needs to be whitelisted by the Sakari support team.
Create a ticket: https://support.sakari.io/hc/en-us/requests/new
Use the Contact Reason and ticket subject of Whitelist Email Domain and include your email domain in the message body.