Hi, your error is die to the fact that you’re using a different version of Gradle than the one recommended by PX4 dev. Follow the below steps to continue your dev process
uninstall previous gradle
$ sudo apt-get remove gradle
install SDK
$ curl -s “https://get.sdkman.io” | bash
$ source “$HOME/.sdkman/bin/sdkman-init.sh”
install gradle version 6.3 ONLY!!!
$ sdk install gradle 6.3
and then install FastRTPS Gen:
$ git clone --recursive https://github.com/eProsima/Fast-DDS-Gen.git -b v1.0.4 ~/Fast-RTPS-Gen
&& cd ~/Fast-RTPS-Gen
&& gradle assemble
&& sudo env “PATH=$PATH” gradle install