Libreoffice can't be used in a ubuntu server with other jmix applications

i have installed libreoffice in my ubuntu server. i want to use it with jmix applications running in the server. only installation should be enough to do this according to jmix documentation. but the following error persists:
ReportingException: Unable to convert to calc_pdf_Export. All attempts failed Report name [Salary summary sheet]
Unable to create Open office components.
io.jmix.reports.yarg.formatters.impl.doc.connector.BootstrapException: Unable to connect to the OO process
Unable to connect to the OO process
java.net.ConnectException: Connection refused

what is the solution to this problem?

I don’t know, but I’m not sure if you qualify as a server admin…
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Points to start:

How is the program started on your server? Does it use the --accept switch. And from the “OO”: Is Open Office expected instead of LibreOffice?
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How old is this documentation? And how/what did you install. You are aware ubuntu uses now snap as default install, wich may not be what your jmix expects…
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EDIT: According to my reading you need to do at least a minimalistic setup: You have to tell the path to LibreOffice. But maybe I found other documentation than you
https://docs.jmix.io/jmix/reports/configuration.html
/EDIT
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One last note: As you use software here, wich is not part of the tdf/LibreOffice-system, please provide some links, if you reference stuff like “jmix documentation”. Especially short names/abbreviations are often not helpful.