Hi,
I've seen your job posting and I'm very interested to complete this task for your full satisfaction. I'm a shopify developer and have created shopify stores and uploaded its products successfully.
The problem yes it's true that it comes with the coding that makes the currency follow on the user's origin or location even if not stated during their login process, the IP address is then noted that reacts with the code that's why the currency follows user's country.
One solution for these is either go your backend and then put a universal currency or make it as US currency for all users, this is the best remedy that I can give you.
Hope to hear from you soon,
Ruel