Grabfood voucher codes suddenly not working

For some reason, I have been having some issues with grabfood voucher codes this year. I have used them before so I know how to use them. So the story is that I have had grabfood voucher codes which expired at the end of the month in Feb 23 and Mar 23. So when I use the app to test the grabfood voucher code before, i.e. on 1st Feb for the voucher code that expires end of Feb 23, I would be able to see that the voucher is valid until 28 Feb 23. However, when I try again near the end of the month, i.e. 26 feb 23, I would see that the voucher code is "invalid or fully redeemed". This has happened to me in Feb 23 and in Mar 23 (fool me twice, shame on me T_T). The codes would work previously when I tested them by entering it in the rewards section. You can enter a code and not click apply, so you will see the value and expiry date, and not actually use it yet. And then when I wanted to use them in the last week of the month, it would suddenly not be working anymore. I wrote down the voucher codes and expiry dates in my phone notes app and they were also printed on the physical cards the voucher codes came on so I am sure I didnt get the expiry dates wrong or the alphanumeric characters of the voucher code wrong. I contacted Grab to ask them if there was some error, but was told that the codes were invalid and to check with the source who supplied me to codes. I did not check with the source as I was pretty sure the grabfood voucher codes were unique as there were printed on physical cards and given to us employees by my company as a token of appreciation.

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With Grab cutting corners here and there recently, I dunno if this is just the cynic in me thinking that a big company like them would find such small ways to screw over the little guy to save costs. I am not sure if I am the only one who experienced this, but if anyone has experienced the same thing, please do share! Maybe the codes were not unique, and this is just a case of my company screwing us workers over. If that is case, just wanna say that I have already just left that company. Haha.