Hi epsragh,
I’ll try to help you on your issue but first I wonder why you want to use the low level message APIs.
Usually, these APIs are internal use in Legato and server/clients development in rather done in a bit higher level. Have a look at daemon developments in Legato code to get a better idea (example: le_cellnet.api, le_spi.api).
Hope this helps,
Regards,