Hello Zero cool,
Please check your code.
As per this code, lw_zrerate_dtl is not getting filled anywhere.
It means that lw_zrerate_dtl is completely blank, hence no update is happening.
So either use columns from zwa_zrerate_dtl during Update(as per your logic) or fill lw_zrerate_dtl before UPDATE.
Warm Regards,
Shyam