To test your HTTP service, the best tool is the Postman which has a GUI interface. The old version is running as part of the Chrome browser but the latest version is a standalone desktop application supports Linux, Mac and Windows.
To install it on Ubuntu Linux 18.04 and up, you can use snap.
snap install postman
Turn off Certificate Verification
As light-4j service has TLS enabled by default with a built-in self-signed certificate, you need either upload the certificate to the postman or simply turn off the certificate verification from settings/General/SSL certificate verification.
Upload the certificate
First, you need to export the certificate from client.truststore with Java keytool command and then you can upload from Settings/Certificates of the postman.