POSID has a conversion exit, your 'LIKE' statement may not work because the system is applying it to the internal format for POSID. Try applying the external conversion exit ("CONVERSION_EXIT_ABPSN_OUTPUT") first to POSID in your table and then using the operator 'CP' instead of like to check the pattern.
i.e.
IF prps-posid CP '123*'..
" <Put your code here>
ENDIF.
Hope that helps...
Cheers,
Katan