You are not going to refuse him. The question is only whether you can find it in March.
Udhaar is one of the payment choices on the bill you were already making, so the goods, the amount and the customer are one record rather than two. Before you agree you can see what he already owes. When he pays, that is another entry — the balance is worked out from the entries and nothing is overwritten, so there is no version of this where a number is quietly corrected.
A line in the book, and it works. What it does not do is add itself up, tell you who has not paid in two months, or survive a flood. The failure mode is not that the book is wrong — it is that nobody reads it until the total is too large to talk about, which is the whole reason udhaar goes bad.
The balance is tracked and the reminders usually work. What is missing is the other half: the sale itself is not in it, so the shop is running two records that have to agree — stock came off a shelf in one place and money went onto a ledger in another. Reminders in this category are also commonly metered, with a free quota and a per-message charge after it.
The columns above describe categories, not products, and that is deliberate. A claim about somebody else's app is true on the day it is written and stops being true the week they ship something — so a page with a rival's name on it ages into a false statement that we then have to be told about. What is described instead is a pattern of behaviour you can check against whatever you are actually using, in about a minute, without taking our word for any of it.
No card and nothing to cancel. Install it, sign in with your phone number, and the shop is yours from the first bill.