What is the correct Xcode build setting for enabling `#if Dev` / `#elseif SIT` Swift compiler flags?

Active Compilation Conditions — not "Other Swift Flags".

Go to Target → Build Settings, search for Active Compilation Conditions, and set the value per configuration:

Configuration	Active Compilation Conditions
Dev	Dev
SIT	SIT
UAT	UAT
Prod	(leave empty)

⚠️ If you add flags to Other Swift Flags instead, #if checks will silently fall through to #else. Values are case-sensitive and must exactly match what you write in Swift.

Leaving Prod empty means the #else branch handles production — the safest fallback pattern.