Web SDK results in 500 error trying to make purchase()

I am having issues with the RC Web SDK.  I followed the instructions to get setup, and have successfully added products to Stripe & added to my existing mobile app offerings.  I can now view my paywall with products:

When I click “continue” for either product it results in an error:

The console shows a 500 error to the RevenueCat API:

POST https://api.revenuecat.com/rcbilling/v1/purchase 500 (Internal Server Error)

qr	@	Purchases.es.js:6824
postPurchase	@	Purchases.es.js:7015
startPurchase	@	Purchases.es.js:4850
ae	@	Purchases.es.js:6398
eval	@	Purchases.es.js:6383
Ei	@	Purchases.es.js:100
eval	@	Purchases.es.js:1782
cr	@	Purchases.es.js:971
eval	@	Purchases.es.js:1782
to	@	Purchases.es.js:766
lt	@	Purchases.es.js:816
ts	@	Purchases.es.js:866
rs	@	Purchases.es.js:852
ns	@	Purchases.es.js:876

When i close the modal this error shows up in the console:

Purchases.es.js:4768 Uncaught (in promise) ce: Unknown backend error.
    at ce.getForPurchasesFlowError (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:4768:12)
    at onError (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:9263:36)
    at HTMLButtonElement.R (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:6435:8)
    at HTMLButtonElement.click (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:5158:36)
    at HTMLButtonElement.fo (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:1803:7)
    at HTMLButtonElement.eval (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:5061:8)
    at eval (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:1122:25)
    at oo (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:1106:12)
    at HTMLButtonElement.a (webpack-internal:///(app-pages-browser)/./node_modules/@revenuecat/purchases-js/dist/Purchases.es.js:1122:14)

What am I doing wrong?  I am under the impression I do not need any additional setup when using this SDK.

Here is my code for making the `purchase()`:

const handleSubscription = async (pkg: Package, email: string) => {
    await Purchases.getSharedInstance().purchase({
      rcPackage: pkg,
      customerEmail: email
    });
  };


// arguments passed to RC purchase():
{
    "pkg": {
        "identifier": "$rc_monthly",
        "rcBillingProduct": {
            "identifier": "prod_RiL5rO2EYYxExK",
            "displayName": "Monthly",
            "title": "Monthly",
            "description": "Monthly Subscription",
            "productType": "subscription",
            "currentPrice": {
                "amount": 599,
                "amountMicros": 5990000,
                "currency": "USD",
                "formattedPrice": "$5.99"
            },
            "normalPeriodDuration": "P1M",
            "presentedOfferingIdentifier": "default",
            "presentedOfferingContext": {
                "offeringIdentifier": "default",
                "targetingContext": null,
                "placementIdentifier": null
            },
            "defaultPurchaseOption": {
                "id": "base_option",
                "priceId": "prc91fefcad308748de8a36",
                "base": {
                    "periodDuration": "P1M",
                    "period": {
                        "number": 1,
                        "unit": "month"
                    },
                    "cycleCount": 1,
                    "price": {
                        "amount": 599,
                        "amountMicros": 5990000,
                        "currency": "USD",
                        "formattedPrice": "$5.99"
                    }
                },
                "trial": null
            },
            "defaultSubscriptionOption": {
                "id": "base_option",
                "priceId": "prc91fefcad308748de8a36",
                "base": {
                    "periodDuration": "P1M",
                    "period": {
                        "number": 1,
                        "unit": "month"
                    },
                    "cycleCount": 1,
                    "price": {
                        "amount": 599,
                        "amountMicros": 5990000,
                        "currency": "USD",
                        "formattedPrice": "$5.99"
                    }
                },
                "trial": null
            },
            "subscriptionOptions": {
                "base_option": {
                    "id": "base_option",
                    "priceId": "prc91fefcad308748de8a36",
                    "base": {
                        "periodDuration": "P1M",
                        "period": {
                            "number": 1,
                            "unit": "month"
                        },
                        "cycleCount": 1,
                        "price": {
                            "amount": 599,
                            "amountMicros": 5990000,
                            "currency": "USD",
                            "formattedPrice": "$5.99"
                        }
                    },
                    "trial": null
                }
            },
            "defaultNonSubscriptionOption": null
        },
        "packageType": "$rc_monthly"
    },
    "email": "myemail@gmail.com"
}

Is there something different for Stripe to know Dev vs Prod environments?