If you are uploading your music from an iOS device, you will need to make sure you select your files from the iOS file browser, or else you may have issues uploading your album cover or audio files, such as seeing an error message saying that "The file you uploaded is zero bytes."
Once you are on the upload form, fill out information as necessary. When you get to the section where you upload artwork, tap on the box where it says "Choose new image". From here you will be given the option to select a photo from your photo library, take a photo, or browse your iOS devices file browser. At this time, in order to upload your artwork from an iOS device you will need to select your artwork file from your devices file browser. Tap on "Browse".
Once you have selected browse, you will be presented with your devices embedded Files app file browser. You can now navigate to where you have stored your files fo upload. For this example, I have stored my audio file and album artwork in the "Downloads" folder on my iPhone.
From here, we can continue down the upload form until we get to the section where we will upload the audio file. When you get to the "Audio file" section of the upload form, tap on "Choose File". You will be presented with the same three options, and again you will need to select "Browse" to take you to the iOS file browser.
Once you have selected your audio file, you should be good to go! If you are experiencing issues, make sure you are storing your files locally on your iOS device instead of in iCloud. The DistroKid upload form does not support cloud uploading at this time, so you will need to upload files directly from your iOS device.