Edit for BlockLauncher 1.9.8: the current suggested MCPE version string for addons is "0.11.1". "0.11.0" is still supported though.
You need to add
<meta-data android:name="net.zhuoweizhang.mcpelauncher.api.targetmcpeversion" android:value="(the MCPE version you tested this addon with)"/>
to your addon's AndroidManifest.xml: for example,
<?xml version="1.0" encoding="utf-8"?>