HI,
Use CRM_MESSEAGE_COLLECT FM to raise your messages if you want to save the message in WEBUI.
Always delete your message using CRM_MESSAGES_DELETE EM before using COLLECT FM if user enters wrong value RAISE error using COLLCET FM. which ever you raise using COLLECT FM need to be deleted if we want to remove the message from WEBUI manually using DELETE FM
Regards,
Deepika.