There are several reasons if you cannot install the APP.
Two main reasons of installation failure after LIAPP protection are as follows.
1) If the APP did not go through Signing
This is the case when you immediately try to install LIAPP-protected APP file after downloading it.
Please make sure you perform Signing before installation.
2) If APK Signature Scheme v2 is applied before LIAPP protection. (Even though you performed Signing)
Those APP files signed via APK Signature Scheme v2 will not be installed if contents are changed.
If you want to use APK Signature Scheme v2, you should use apk files (unsigned apk) or sign via existing methods to apply LIAPP, then re-sign with APK Signature Scheme v2 after.
For more information on APK Signature Scheme v2, please refer to Official Android website.
If none of the above is your case and you still fail to install, please send the LIAPP-protected APK file to firstname.lastname@example.org.