I am having the same issue referenced in this post: Upload images to S3 from Mobile Input - #3 by Daniel_Weinstock
The issue only occurs when usign Retool Mobile from my iOS phone. The version I am running is Retool Mobile v3.183.0 Build 2132.
The Content-Type is not being set when doing an S3 Upload from my phone. I have tried deriving the content-type by extracting the details from the file and also hardcoding it. It is stripped when I inspect the image in the S3 bucket.
If I use the same app on my browser emulating mobile, it works fine.