It will be reflected on your 7th month bill statement. E.g. If the 1st supplementary line is activated on 5th January and therefore, the discount will appear in your July bill statement.
The following is an example on how to measure the discount:
[Principle line (U38)+Supplementary Line] X 50%
Hence,
[RM38+RM10] X 50%
= RM48 X 50%
= RM24, Discount Entitle
The credit limit for a supplementary line will be shared with the principal line. E.g. If the principal has subscribed to U38, therefore the total limit of the principle and supplementary line is RM150.