Hi Joao
I am the Product Manager for SAP Sourcing responsible for the Platform related topics with the application.
As I mentioned SAP Sourcing On Premise doesn't support LJS. This means that the Support will not be able to help or be able to provide any guidance on this matter, or provide any assistance for other issues that you might run up against, since you are implemented on an unsupported platform.
I would also like you to know that LJS is just a container and there is no native support for JMS, and doesn't have the appropriate JMS bundles included. My sincere suggestion and recommendation would be to have SAP Sourcing installed on SAP Sourcing 7.3
Best
Amish Shah