Initiate Checkout with Credit Key from a non e-commerce integration.
If you utilize the mode param with a value of "link" you can send a hyperlink to the email address or phone number of the billing address user on the Order. You may specify the contact method in the merchant_data param ex: contact_method: 'email'|'phone'. Additionaly, if merchant_data.cc_rep is true, the CSR rep will also be notified.
See more specific details of each option in merchant_data in the definition for begin_standalone_checkout_request.
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