If you intend on keeping the pants for yourself for an extended period of time, I would recommend sourcing a trusted local tailor. Have acr ship the zip or replace with another YKK or something accessible. Depending on how the zip is broken, it shouldn't be too difficult of a fix.
If you send back to acr, you would know that the craftsmanship is up to factory standard. This is especially a good idea if you intend to resell, but who knows when you'll get them back.
I typically buy with the intentions of keeping for as long as humanly possible, so I either repair myself or find a suitable tailor. Supporting local and also not flying a pair of pants across the planet is good for everyone.
Best of luck!