if i would like to pay zalora or prestomall via grabpay, do i need to topup first into the grabpay credits or it can deduct directly from credit card via grabpay?

Unable to open the link from my side 

Just want to reconfirm:

1) If purchase something online and rewarded with grabpoints, later return goods partially and got refunded, will the rewarded points be deducted?

2) Do we get grabpoints if use grabpay for payment to non-grab services like 3rd party merchants?

I have done some calculations before and Grab point system seems to have the most value compared to other point systems.
However grab's voucher exchange is very limited.

For example, if you want to exchange the point for groceries, grab only allows Jaya grocer. Other credit card point rewards point systems allows Alot of options.
Although grab allows you to exchange for voucher with much lower points compared to other systems, your choice is very limited as of today.

Perhaps I haven't figure out the best way to utilize the points yet.