Why the hell did you put the promo code field on the login form? What type of fucking eCommerce site are you?

Where should it really be?

I would say it should be inputted at checkout. Usually that's ok.

But what if it's not a normal eCommerce site? What if it's an eCommerce site for accommodation or tickets? Where you would put it then?

@joas I’ve been trained to look for it shortly before I enter my credit card number.

I don't know, why did you put the promo code on the login form?

...wait, this isn't a joke.

@joas usually at payment screen, anywhere else is just odd unless it's like product specific and might make sense to input it at the product page, but even then that's an anti pattern.

So really, on the checkout before payment is the only sane place to put it.