This is very late, but I ran into the same error. I saw a hint at https://community.splunk.com/t5/All-Apps-and-Add-ons/Unable-to-initialize-modular-input-quot-mqtt-quot-defined-inside/td-p/131063 I also found a page about troubleshooting add-ons: https://docs.splunk.com/Documentation/AddOns/released/Overview/Troubleshootadd-ons Which allowed me to find the following log from the add-on for more information: 07-20-2020 06:43:40.050 +0000 ERROR ModularInputs - <stderr> Introspecting scheme=mqtt: java: symbol lookup error: java: undefined symbol: JLI_StringDup And then I found this bug: https://bugs.launchpad.net/ubuntu/+source/openjdk-lts/+bug/1882208 So I downgraded to openjdk-8 and all is well for me (I was on openjdk-11). I see that you're running jdk-12, which is likely to be your problem.
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