Unable to upload header logo

I’m using a child theme for Iconic One theme. When I tried to upload a logo in Appearance > Customize Iconic One > Logo, nothing happened. I used both “drop a file here” and “select a file” options yet, no image could be uploaded. Is there a default image size?

Can anyone please assist me with this issue? Thank you.

(FYI, I could upload featured images in my posts)