Here is the message they provided
Guideline 2.1 - Performance - App Completeness
Issue Description
The app exhibited one or more bugs that would negatively impact App Store users.
Bug description: "Failed to connect to server" error prompt during login
Review device details:
Device type: iPad Air (5th generation)
OS version: iPadOS 18.1.1
Next Steps
Test the app on supported devices to identify and resolve bugs and stability issues before submitting for review.
frommomo
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We've used all kinds of combinations and it's not a problem