This is a known issue with AutoSSL, and usually, the SSL certificate actually does install correctly. Before putting in a support ticket, check to see if it actually did fail, like so:
- In Chrome, navigate to your website. Preferably a part that uses SSL like a sign-in page, cart or checkout. Depending on how your website is configured, you may be able to load your homepage over SSL by adding "HTTPS" to the beginning of it (https://mywebsite.com).