If you have submitted your podcast to Apple Podcasts. Please first make sure your artwork meets the requirements by Apple below.

"Artwork must be a minimum size of 1400 x 1400 pixels and a maximum size of 3000 x 3000 pixels, 72 dpi, in JPEG or PNG format with appropriate file extensions (.jpg, .png), and in the RGB colorspace."

It might take time for your artwork to be updated on Castbox. Normally, your artwork will be updated within two days after it has been updated on iTunes.

Please contact podcaster@castbox.fm if anything goes wrong.