You can see if your server can downgrade to php6 or below.
If you need to run php7, then you need to upgrade eCart to v6 for mySQLi support.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.