Pro Sites / Stripe Error - "The Stripe customer could not be created. Please try again."

I'm trying to set up Stripe as the payment gateway for Pro Sites and getting this error on the checkout screen when processing a payment: "The Stripe customer could not be created. Please try again."

I'm currently using Stripe in test mode. API and Webhooks seem to be working correctly, the subscription plans are in sync but the coupon codes aren't though.

Signup is being handled through Ultimate Facebook plugin, requiring registration through FB. I tested the checkout process with an account created with the plugin disabled, still nothing.

It's an enigma wrapped in a riddle, help

Thank You