The "mystrikingly.com" URL is the address of your site. After creating your site, you get a free Strikingly URL in this format:
1. Go to your site editor and click Settings > Domains.
2. Update the URL in the "MyStrikingly.com URL" field (only lowercase alphanumeric and '-' are allowed).
3. Click "UPDATE".
Tip: You can connect your own domain (e.g. www.mydomain.com) to your Strikingly site after upgrading. If you haven't had a domain yet, the Strikingly Yearly plan and above can claim one free domain for the first year: Strikingly Domain: Buy & Register Your Own Custom Domain.