I get this on the 1.9.4 version of the app, and running iOS 9.3.3:
[exec dpkg -i] ...
bash-4.0$ Filza dpkg -i "/var/mobile/Documents/com.day03.mathlearnerunlockedbyday03_0.0.1-1 debug_iphoneos-arm (1).deb" ;
(Reading database ...
(Reading database ... 5%
(Reading database ... 10%
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(Reading database ... 90%
(Reading database ... 95%
(Reading database ... 100%
(Reading database ... 7921 files and directories currently installed.)
Preparing to unpack .../com.day03.mathlearnerunlockedbyday03_0.0.1-1 debug_iphoneos-arm (1).deb ...
Unpacking com.day03.mathlearnerunlockedbyday03 (0.0.1-1+debug) ...
dpkg-deb (subprocess): unable to execute decompressing archive member (xz): No such file or directory
dpkg-deb (subprocess): subprocess decompressing archive member returned error exit status 2
dpkg-deb: error: subprocess <decompress> returned error exit status 2
dpkg: error processing archive /var/mobile/Documents/com.day03.mathlearnerunlockedbyday03_0.0.1-1 debug_iphoneos-arm (1).deb (--install):
subprocess dpkg-deb --fsys-tarfile returned error exit status 2
Errors were encountered while processing:
/var/mobile/Documents/com.day03.mathlearnerunlockedbyday03_0.0.1-1 debug_iphoneos-arm (1).deb
bash-4.0$