Leave/ unavailable days as a casual

Need advice from fellow Woolworths employees Been working as a casual for the past 5 months. Initially only wanted 8-16 hours a week due to current circumstances in my life. Was told when I started to just submit my availability on WorkJam etc and if I put unavailable on certain days I wouldn’t be rostered on. About 2 months ago I put unavailable on this coming long weekend as I have a wedding to attend. Thought all was good until I opened my app and saw I was rostered on days I clearly said was unavailable. Spoke to my manager straight away and explained I am away etc. he has then informed me that I need to submit for holiday leave on success factors ? First I’m hearing of this Just wondering what other people have as experiences here and whether this is normal for a casual ? And should my availability on WorkJam schedule even matter ?