Ecwid is designed to work on any platform. Ecwid supports responsive layout that allows Ecwid shops to adapt to different screens.
Facebook has certain restrictions hindering the work of applications on mobiles, and it impacts all Facebook apps, not only Ecwid.
Please see the detailed reasons here: https://support.ecwid.com/hc/en-us/articles/115002965485
In such cases, we commonly recommend our customers to post a link to their Ecwid Starter Site (yours is always available in your Ecwid Control Panel → Settings → General → Starter Site) somewhere on their Facebook store page, so that the customers viewing the site from mobiles could open your store and make orders. Starter Site has a fully responsive layout, so it will be displayed accurately on mobiles. You can check its appearance in our Demo store.
To get your store visible on mobile devices in Facebook, please follow the steps below:
1) Get your Starter Site link by going to your Ecwid Control Panel → Settings → General → Starter Site and copying the link below "Starter Site URL".
2) Go to your Facebook page and click "+ Add a button"
3) Choose "Shop Now" from the drop down list
4) Add a link to your Starter Site and click "Add Button"
Now the "Shop Now" button will lead to your responsive store page where your customers will be able to shop from any mobile device.
Main article about Facebook: https://support.ecwid.com/hc/en-us/articles/207806665-Facebook