are you perhaps using a ktor version based on 1.3-m1? (just guessing)

No as I said I'm using Stable channel and plugin version is 1.2.70-blabla

it sounds like one of your dependencies is pulling in 1.3-M1, in which case channel and plugin version don’t matter.

Well it's weird because apart from updating plugins (kotlin and kotlinx.serialization) and updating kotlin version to 1.2.70 in gradle I didn't change anything

running

gradlew dependencies

would be a good start

Thanks a lot! Looks like ktor version I used was for 1.3. Downgrading solved the issue

👍