I remember seeing this question from other members but I don't remember how it was addressed.... sorry.Thanks @YVR123 for your response ! I've actually gone through these instructions, however it says - If you don’t have a family name on your passport or travel document, enter all given names in the family name field and leave the given name blank.
But the problem is - in the pdf IMM5406 form, it seems both are mandatory to fill, otherwise it gives error when you click Validate !
Secondly they also write in another instruction not to leave any field blank
Thanks