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DoorDash apparently using client side source of truth

news.ycombinator.com

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DoorDash apparently using client side source of truth

#1

Post by dkarp »

I order from Doordash a couple times a week because I am lazy and it's convenient. I get a dashpass through my credit card which makes it less extortionate.

Last week I saw that I was being charged the full service fee and delivery fee on my order. I also saw that it had been going on for weeks and I hadn't noticed (should be paying more attention...)

Here's the interesting part. When I contacted support, they said I should delete the app and re-install it. After doing so, the dashpass was working correctly.

I've worked on plenty of checkout systems and they always used the backend as source of truth, even if they did some calculations on the frontend for UI reasons. I can't see how Doordash can be doing that if re-installing the app was enough to fix my dashpass. Surely even if the app showed the incorrect value then the backend should have known I had a dashbpass and billed me correctly.

Anyway, now I have to email doordash and try to get them to refund service charges and delivery fees for a month of orders...

Re: DoorDash apparently using client side source of truth

#2

Post by rappatic »

Did you check your credit card statement to confirm that you were actually being charged the incorrect price (incl. the service charges and delivery fees)? Is it possible that the client calculates the price shown in the UI itself while the backend calculates it separately to do the actual billing, and there was simply a discrepancy between the calculations until you re-installed the app? Of course if you did check your credit card statement then there is definitely something weird going on.

Re: DoorDash apparently using client side source of truth

#4

Post by explorigin »

BlueGh0st wrote: post #3

I remember being able to put in a negative tip to zero out the order cost, checkout, and tip in cash. So I don't find this shocking.

Considering what we're talking about, a negative tip might have actually charged the driver. Hope you tipped in cash more than you negative tipped. :-P

Re: DoorDash apparently using client side source of truth

#6

Post by brianhama »

This likely has to do with how in app purchases are processed. Theres a few ways to process in app purchases, but one of them involves the OS proving the app with a signed receipt which the app then sends to the server. Likely a bug prevented this receipt from being sent, but when the app was reinstalled it would have been presented with the signed receipt again since it had not been marked as consumed yet.

Re: DoorDash apparently using client side source of truth

#7

Post by lights0123 »

brianhama wrote: post #6

This likely has to do with how in app purchases are processed. Theres a few ways to process in app purchases, but one of them involves the OS proving the app with a signed receipt which the app then sends to the server. Likely a bug prevented this receipt from being sent, but when the app was reinstalled it would have been presented with the signed receipt again since it had not been marked as consumed yet.

DashPass doesn't use in-app purchases, they do their own billing.

Re: DoorDash apparently using client side source of truth

#8

Post by dkarp »

rappatic wrote: post #2

Did you check your credit card statement to confirm that you were actually being charged the incorrect price (incl. the service charges and delivery fees)? Is it possible that the client calculates the price shown in the UI itself while the backend calculates it separately to do the actual billing, and there was simply a discrepancy between the calculations until you re-installed the app? Of course if you did check y…

Good question, I just checked my credit card statement and they billed what the UI said they would...

I can also still see the orders in the my order history with the incorrect amount

Re: DoorDash apparently using client side source of truth

#9

Post by sublinear »

I'm not sure it's "client side source of truth" as much as it's just a bug with the dashpass status being lost occasionally unless you go into the payment settings under the account and select your credit card again.

This bug happens to me every few months and I know when it happens because it's clearly displayed in the checkout screen that the dashpass discount is not being applied to the total. I'll see delivery fees and other fees applied that are usually waived or discounted.

There's a similar bug on both doordash and uber eats where my delivery address gets reset.

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