Custom Discount Setup using Promotions + Custom Field Questions

[coderreco]

Client needs to run a day of discounts that is allows customers to apply multiple coupons to their carts using a code. Seems that the easiest way to apply this is by building a custom discount service that uses promotions with a custom field added to the promotions model for the coupon code itself. Then I validate the coupon code and add the the promotion to the cart using the backend api using swell.post("/carts", {"promotion_ids": [{/*id of promotion validated by coupon code custom field etc*/}]}, right?

I have a couple of questions regarding disabling the default behaviour for promotions:

How can I create a basic percentage or fixed product/category promotion and not have it auto-apply before a user inputs the related code? This is an excerpt from @ericingram on another post:

You can set a very high "minimum order subtotal" so that it won't apply automatically. Also note that from the backend API, you would need to pass $promotions: true to automatically apply promotions, so if you don't need it work to automatically any way then that's another option

I get the part about setting a very high "minimum order subtotal", but does that mean if the cart is still below that very high "minimum order subtotal" and I post it to my cart, will the discount apply correctly? If I recall correctly when I used "minimum order subtotal" on promotions in the past, if a customer passes that minimum threshold the promotions get's applied, but if they remove items that brings them back below the "minimum order subtotal", the promo stays on the cart but the discount is removed unless they bring the cart back over the "minimum order subtotal" threshold.

Also, what does $promotions: true do exactly, and where do I pass it? The majority of the integration uses the frontend-api for interacting with the cart, will this interfere with that at all?

Thanks in advance!

[ericingram]

It sounds like you're looking to use promotions as a pseudo coupon where the user can apply them manually?

In that case I would use the custom field as you described and apply the promotions related to the code using the example backend API call with promotion_ids.

The operator $promotions: true is used to automatically apply all promotions that meet order criteria, so that's not what you want. Instad (again using the backend API) set promotion_ids according to the codes entered and it should just work.