You can read the official announcement here on Maybank website.
I found out about this when I was about to make an online purchase but my card got denied during the checkout process.
How To Get Maybank Debit Card Online Purchase Working Again?
To enable E-Commerce transaction for online purchases, you need to call MGCC (Maybank Group Customer Care) at 1300 88 6688 for immediate on the spot activation.
During the call, I was asked some questions to verify my Maybank account such as what is my identity card number and which Maybank branch did I registered my account with, etc.
Then I was asked whether I want to activate my debit card for foreign transactions. This should be your concern if you plan to do some Ecommerce purchases from someone or merchants that are not in Malaysia.
If you choose to also activate the foreign transactions, you will be asked for how long do you want it activated. Maximum is 1 year. You will be mentioned of the amount of maximum transaction per day which you can change according to your preference.
Once you have enabled your account for online purchases and later you wish to disable it again for some reasons, you have to call MGCC again and let them know about the deactivation request.
If Maybank updates their methods for activating this, you can mention it in the comment section below and I will update this accordingly.