How to locate apk file using bitbucket-pipelines?

I'm using BitBucket-pipelines for Android CI. I'm trying to export the artifact (generated apk) to the downloads section of the project.

My bitbucket-pipelines.yml is as follows, but it can't locate the apk file

image: openjdk:8

pipelines:
default:
- step:
    caches:
      - gradle
      - android-sdk

    script:
      # Download and unzip android sdk
      - wget --quiet --output-document=android-sdk.zip https://dl.google.com/android/repository/sdk-tools-linux-3859397.zip
      - unzip -o -qq android-sdk.zip -d android-sdk

      # Define Android Home and add PATHs
      - export ANDROID_HOME="/opt/atlassian/pipelines/agent/build/android-sdk"
      - export PATH="$ANDROID_HOME/tools:$ANDROID_HOME/tools/bin:$ANDROID_HOME/platform-tools:$PATH"

      # Download packages.
      - yes | sdkmanager "platform-tools"
      - yes | sdkmanager "platforms;android-27"
      - yes | sdkmanager "build-tools;27.0.3"
      - yes | sdkmanager "extras;android;m2repository"
      - yes | sdkmanager "extras;google;m2repository"
      - yes | sdkmanager "extras;google;instantapps"
      - yes | sdkmanager --licenses

      # Build apk
      - chmod a+x ./gradlew
      - ./gradlew assembleDebug

      # Saving artifact
      - curl -X POST "https://${BB_AUTH_STRING}@api.bitbucket.org/2.0/repositories/${BITBUCKET_REPO_OWNER}/${BITBUCKET_REPO_SLUG}/downloads" --form files=@"**/*.apk"


definitions:
  caches:
     android-sdk: android-sdk

The issue is in

- curl -X POST "https://${BB_AUTH_STRING}@api.bitbucket.org/2.0/repositories/${BITBUCKET_REPO_OWNER}/${BITBUCKET_REPO_SLUG}/downloads" --form files=@"**/*.apk"

I've also tried the following instead of **/*.apk

./app/build/outputs/apk/*.apk

But so far, nothing can locate the apk.

Has anyone faced this issue before? I'm just getting into CI with Android and would be grateful if someone could help.

I was able to resolve the issue by adding an artifacts tag after the build step. Then to publish the apk file I had to point to the specific file (path respective to the parent folder).

My bitbucket-pipelines.yml file is as follows now.

image: openjdk:8

pipelines:
  default:
    - step:
      caches:
        - gradle
        - android-sdk

      script:
        # Download and unzip android sdk
        - wget --quiet --output-document=android-sdk.zip https://dl.google.com/android/repository/sdk-tools-linux-3859397.zip
        - unzip -o -qq android-sdk.zip -d android-sdk

        # Define Android Home and add PATHs
        - export ANDROID_HOME="/opt/atlassian/pipelines/agent/build/android-sdk"
        - export PATH="$ANDROID_HOME/tools:$ANDROID_HOME/tools/bin:$ANDROID_HOME/platform-tools:$PATH"

        # Download packages.
        - yes | sdkmanager "platform-tools"
        - yes | sdkmanager "platforms;android-27"
        - yes | sdkmanager "build-tools;27.0.3"
        - yes | sdkmanager "extras;android;m2repository"
        - yes | sdkmanager "extras;google;m2repository"
        - yes | sdkmanager "extras;google;instantapps"
        - yes | sdkmanager --licenses

        # Build apk
        - chmod a+x ./gradlew
        - ./gradlew assembleDebug

      artifacts:
        - app/build/outputs/apk/debug/*.apk

  - step:
     script:
        # Saving artifact
        - curl -X POST "https://${BB_AUTH_STRING}@api.bitbucket.org/2.0/repositories/${BITBUCKET_REPO_OWNER}/${BITBUCKET_REPO_SLUG}/downloads" --form files=@"app/build/outputs/apk/debug/app-debug.apk"


definitions:
    caches:
        android-sdk: android-sdk