Jar timestamping doesn't work


I’m using Timestamp Server And Stamping Protocols | Sectigo® Official to timestamp jars with jarsigner running a Maven build. The plugin config for the jarsigner plugin consists the following lines:

When I test the resulted jar files by running a jnlp, the timestamp doesn’t seem to work, because setting the time beyond the expiration of the code signing certificate triggers an expiration warning in Java.
If I type the server URL in the browser, it downloads a file with the following content “000.0%#Bad request format or system error.”, but maybe that’s normal, I’m not sure.
Is there any problem with the server or am I missing something?