65K Reference Limit
Unity: All versions | Appodeal SDK: All versions
The error "Cannot fit requested classes in a single dex file" happens if the number of method references exceed the 65K reference limit.
The error example from Unity Editor Log:
stderr[ D8: Cannot fit requested classes in a single dex file (# methods: 136481 > 65536) FAILURE: Build failed with an exception. * What went wrong: Execution failed for task ':launcher:transformDexArchiveWithExternalLibsDexMergerForRelease'. > com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives: The number of method references in a .dex file cannot exceed 64K. Learn how to resolve this issue at https://developer.android.com/tools/building/multidex.html
To solve the error enable Multidex support.
For Unity 2019.2 and versions below:
Add Multidex support to your project. Follow this guide to add Multidex.
For Unity 2019.3 or higher:
Go to File → Build settings → Player Settings → Player → Minimum API level and set up minimum API level to 21 or higher, where Multidex is enabled by default.