When you try and upload a custom skin from photos on an iPhone, the client rejects and says "This is not a Minecraft skin silly", even though it is. If I take that image and use it on Bedrock Windows 10 edition, it accepts it. I believe it happens on Xbox and Switch too, just not Win10.

The skins I've tried are attached, I've tried 64x32, 64x64 and 128x128, all rejected. I've looked at other issues on this Jira and seems that this has been an issue in the past but was resolved, looks like it's back.