Do you have a build log URL that shows the problem you are describing here? Are you listing licenses to accept? https://docs.travis-ci.com/user/languages/android#Dealing-with-Licenses

This issues is documented in several places:
https://code.google.com/p/android/issues/detail?id=212128
http://kechengpuzi.com/q/s37615379
http://stackoverflow.com/questions/37615379/travis-ci-build-doesnt-work-with-android-constraint-layout

I can't find/don't know what licenses I need to add to my Travis build to make it compile.

I forgot to update this issue, there's been a fix for a while now:

before_install:
  - mkdir "$ANDROID_HOME/licenses" || true
  - echo -e "\n8933bad161af4178b1185d1a37fbf41ea5269c55" > "$ANDROID_HOME/licenses/android-sdk-license"
  - echo -e "\n84831b9409646a918e30573bab4c9c91346d8abd" > "$ANDROID_HOME/licenses/android-sdk-preview-license"

According to documentation all license should be accepted per default. Travis doesn't do that for ConstraintLayout. Also manually setting the license hash results in a failing build.

Above comments also strugle with the setup as commits are marked with a red cross.

All solutions mentioned here are failing other than the one that @wolkenschieber mentioned. Thanks alot for the fix, finally my builds are running 😄

PR Link: https://github.com/edx/edx-app-android/pull/1065 which includes the fix (Exact commit edx/edx-app-android@fe06b43)