sometimes small merchants can't make change. Like grab drivers and and small street stalls, so scan pay is convenient. Or you don't want to carry large amounts of cash on you. Like I said, the app didn't work for me the 2 times I tried to use it.
I did the process on my phone. But after loading all the documents, the verification of upload for larger files didn't work. When I checked on my friend's laptop, it was all correct and uploaded. So I proceeded with payment and was approved.