I figured it out. Sorry I can’t find where to delete the topic. I asked Grok to explain the issue: “GarageBand on iPad has non-standard or Apple-specific headers/metadata that cause web platforms like Manifold Studio to detect its MIME type as audio/x-wav instead of the expected audio/wav (for WAV files) or audio/mpeg (for MP3 files), triggering a strict validation error that prevents saving the instance.” I used an online file converter to correct the issue. Thank you!