So is Amazon Pay just arbitraging Stripe's standard 2.9%?
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“Under the new agreement, Stripe will become a strategic payments partner for Amazon in the US, Europe, and Canada, processing a significant portion of Amazon’s total payments volume across its businesses, including Prime, Audible, Kindle, Amazon Pay, Buy With Prime, and more,” the Stripe post said.
Amazon Pay isn't working for free, they are arbing the spread between 2.9 and 2.1.