Unable to upload image

I chose the Unicorn template but not able to upload or replace any image. It says filename error but I have renamed the files as per the requirement, still it won’t let me upload. I’m still on free plan and I plan to buy Unicorn template. If you could tell me how it will work (image loading).

I’m on Safari, tried on Chrome. Tried in a different laptop as well.

I am having same error