JS API returns customer details in live mode but not test mode

I’m using the following code

await Snipcart.api.customer.fetchDetails()

When using it with my Test API Key, it properly returns the customer details. However, when using it the Live API Key, it returns empty.

Can someone point me in the right direction of what’s going on? I don’t see anything documentation for fetchDetails() in the JS API documentation.

Thank you.