Most social media platforms do not accept HTML5 design uploads, so when you export your design for social media you should export static JPEG images.

To export static JPEG images for a Social media platform, open the Export panel on the right-hand side of the editor and open the Social tab.

After opening the Social tab, select the sizes you'd like to export, and then click 'Export Design (.ZIP)'. 

If there are animations applied to your design, Flexitive will export a static image of the last frame of your animation sequence for the design.