add this into your build.gradle(module app)
packagingOptions{ exclude 'AndroidManifest.xml' exclude 'lib/arm64-v8a/libcardioDecider.so' exclude 'lib/arm64-v8a/libcardioRecognizer.so' exclude 'lib/arm64-v8a/libcardioRecognizer_tegra2.so' exclude 'lib/arm64-v8a/libopencv_core.so' exclude 'lib/arm64-v8a/libopencv_imgproc.so' exclude 'lib/armeabi/libcardioDecider.so' exclude 'lib/armeabi-v7a/libcardioDecider.so' exclude 'lib/armeabi-v7a/libcardioRecognizer.so' exclude 'lib/armeabi-v7a/libcardioRecognizer_tegra2.so' exclude 'lib/armeabi-v7a/libopencv_core.so' exclude 'lib/armeabi-v7a/libopencv_imgproc.so' exclude 'lib/mips/libcardioDecider.so' exclude 'lib/x86/libcardioDecider.so' exclude 'lib/x86/libcardioRecognizer.so' exclude 'lib/x86/libcardioRecognizer_tegra2.so' exclude 'lib/x86/libopencv_core.so' exclude 'lib/x86/libopencv_imgproc.so' exclude 'lib/x86_64/libcardioDecider.so' exclude 'lib/x86_64/libcardioRecognizer.so' exclude 'lib/x86_64/libcardioRecognizer_tegra2.so' exclude 'lib/x86_64/libopencv_core.so' exclude 'lib/x86_64/libopencv_imgproc.so' }
and add dependencies
dependencies { compile fileTree(include: ['*.jar'], dir: 'libs') compile 'com.android.support:appcompat-v7:23.1.1' compile 'com.paypal.sdk:paypal-android-sdk:2.14.1' }

add this into your build.gradle (module app) file.
dependencies { compile 'com.paypal.sdk:paypal-android-sdk:2.14.1' }
don't add any jar file. and in same file add this
android{ packagingOptions{ exclude 'AndroidManifest.xml' exclude 'lib/arm64-v8a/libcardioDecider.so' exclude 'lib/arm64-v8a/libcardioRecognizer.so' exclude 'lib/arm64-v8a/libcardioRecognizer_tegra2.so' exclude 'lib/arm64-v8a/libopencv_core.so' exclude 'lib/arm64-v8a/libopencv_imgproc.so' exclude 'lib/armeabi/libcardioDecider.so' exclude 'lib/armeabi-v7a/libcardioDecider.so' exclude 'lib/armeabi-v7a/libcardioRecognizer.so' exclude 'lib/armeabi-v7a/libcardioRecognizer_tegra2.so' exclude 'lib/armeabi-v7a/libopencv_core.so' exclude 'lib/armeabi-v7a/libopencv_imgproc.so' exclude 'lib/mips/libcardioDecider.so' exclude 'lib/x86/libcardioDecider.so' exclude 'lib/x86/libcardioRecognizer.so' exclude 'lib/x86/libcardioRecognizer_tegra2.so' exclude 'lib/x86/libopencv_core.so' exclude 'lib/x86/libopencv_imgproc.so' exclude 'lib/x86_64/libcardioDecider.so' exclude 'lib/x86_64/libcardioRecognizer.so' exclude 'lib/x86_64/libcardioRecognizer_tegra2.so' exclude 'lib/x86_64/libopencv_core.so' exclude 'lib/x86_64/libopencv_imgproc.so' } }