Hi there Jenko89,
Thanks for reaching out and welcome aboard!
When you as a Duo manager invite your wife as described here, she needs to just open the invitation, log into her account and give the address exactly as you have configured it in the Duo subscription. If she is asked for a payment method, she's most like ended up on the wrong page. What exactly have you tried thus far? Can you send us a screenshot of the exact message that she receives?
We'll be keeping an eye out for your response.
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