Goal

Here you’ll set the icon your app shows on the home screen, the App Store, and Google Play — and you’ll do it in a way that keeps your iOS build safe from Apple error 90717 (“Invalid large app icon… can’t be transparent or contain an alpha channel”).

You won’t need to flatten anything yourself first. MAM strips out the alpha channel for you the moment you save. Below: what to upload, what that background color is actually for, and why the two together are what keeps Apple happy.

Prerequisites

• An admin account with access to Mobile App Mgr → Publish App (the App Icon panel lives here).
• A square PNG icon image, at least 1024×1024 pixels. PNG is required — other formats are not accepted by the icon flattening step.
• A decision about your background color (you can change it later). This is the solid color that will sit behind any transparent areas of your icon. See Step 3 for why it matters.

If your icon is already fully opaque (no transparent pixels anywhere), the background color won’t show up at all — but it’s still worth setting one, just to be safe.

Why this matters (the short version)

Apple rejects your large app icon the moment it detects an alpha channel — the part of a PNG that stores transparency — even one that’s fully opaque, even when your art shows no transparency at all. It’s a frustrating one to get caught by late, because the icon usually looks completely fine.

MAM takes that risk off your plate. When you save the App Icon panel, it composites your PNG onto the solid background color you picked and writes back a flat, opaque PNG with no alpha channel at all. By the time Fastlane hands the build to Apple, your icon is already in the shape Apple wants. You get to design freely; MAM handles the App Store’s pickiness for you.

Steps

1. Open the App Icon panel

Go to Mobile App Mgr → Publish App and find the App Icon panel. You only need to upload one image here — the panel notes that “The app icon is automatically resized for all devices,” so MAM generates every size it needs from that single file.

2. Upload your icon

This is the source image everything else gets built from, so it’s worth getting right. Click the image picker (it reads “Click to select app icon” when empty) and choose your square 1024×1024 PNG from the Media Library, or upload a new one.

A few rules matter here:

• Square. Use the same width and height.
• At least 1024×1024. Smaller icons fail the publish checklist — if yours is too small, the App icon checklist item shows “App icon must be at least 1024×1024 pixels.”
• PNG only. The flattening step only knows how to process PNGs; upload anything else and it gets skipped, which means it could reach Apple in the wrong format.
• Don’t add rounded corners or shadows yourself. Apple and Android already apply their own corner masking, so just supply a full-bleed square and let them handle it.

3. Choose a background color

Next, set the Background Color with the color swatch under the picker. It defaults to white (#ffffff).

Think of this as the color MAM paints behind your icon when it flattens the file — any pixel that’s transparent or semi-transparent gets blended onto it:

• If your icon is edge-to-edge opaque art, this color never actually shows, so pick anything (white is fine).
• If your icon has transparent areas — say, a logo on a transparent canvas — this becomes the solid fill behind it. Choose something that matches your brand and looks right behind the logo, because that’s exactly what your users will see.

Getting this color “wrong” won’t get your app rejected — the only consequence is that the transparent parts of your icon turn that color instead of whatever you had in mind.

4. Save the panel

This is the step that actually does the flattening, so don’t skip it even if everything looks right already. Click Save App Settings at the bottom of the Publish App page. If your icon or your background color changed, MAM automatically flattens the icon on save: it draws your background color across the full canvas, composites your PNG on top of it, and overwrites the stored file as an opaque PNG with no alpha channel. It then regenerates the image’s metadata so the flattened version is the one used everywhere from here on.

Nothing to re-upload or re-export on your end — it all happens behind the scenes the moment you hit save.

5. Confirm it’s done on the publish checklist

Worth double-checking before you move on. Back on the publish checklist, the App icon item under App information should now show as complete, with no “missing” or “too small” warning. If it still flags too small, swap in a larger square PNG and save again.

6. Publish

From here it’s automatic: when you submit the app, Fastlane uploads the already-flattened, opaque icon. Because the alpha channel was already stripped out at save time, Apple’s icon check passes and you sidestep the 90717 rejection entirely.

Troubleshooting

• The icon still has transparency after saving. The flatten step only runs for PNG files at most 4096×4096, so check that your upload is genuinely a PNG and not an oversized export or a JPG/WebP that got renamed to .png. Fix that and re-save.
• Apple still rejected for 90717. Check that the build you submitted was generated after you uploaded and saved the icon — if you changed the icon but didn’t re-save the App Icon panel, the flatten never ran. Re-save, then publish again.
• Transparent areas turned an unexpected color. That’s just the background color showing through. Reopen the App Icon panel, pick the color you actually want, and save — changing the background color re-triggers the flatten.
• Icon looks pixelated on device. That points to a low-resolution source image. Upload a crisp 1024×1024 (or larger square) PNG — MAM can downscale for smaller sizes, but it can’t add detail that was never there to begin with.

What’s next

• Set your Launch Screen next — MAM can auto-generate a splash image from this same icon plus a background color, or you can upload your own.
• Fill in your App name and App description for the store listings (the remaining items in the App information section of the checklist).
• Work through the rest of the Publish App checklist, then submit.

Related

• Set your app’s launch screen (splash)
• Submit your app for publishing
• Publish checklist: what each item means