I was declined using Apple pay to buy crypto because Apple pay said incorrect merchant info What does that mean?

Hi, and welcome to the Apple Community.

Re: Apple pay said incorrect merchant info What does that mean?

Seems the merchant may not offer Apple Pay, or is not giving Apple the correct info. or is not registered with Apple.

Check : Countries and regions that support Apple Pay – Apple Support

Apple Support's online article: Paying with cards using Apple Pay – Apple Support

Eg: says:

"Apple Pay on the web requires that all participating websites register with Apple.

After the domain is registered, domain name validation is performed only after Apple issues a TLS client certificate.

Websites supporting Apple Pay are required to serve their content over HTTPS".

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Re: How to use apple pay to buy crypto at an exchange ?

See if following the guidance in Apple Support's article helps.

Recognise symbols for Apple Pay: Learn where to use Apple Pay – Apple Support

How to: Make purchases using Apple Pay – Apple Support

All the best :-)