I now have a bank card issued by my bank. I have not experienced any difficulties with it. They provided me with a debit card to retrieve funds from their cash machine if I need it. The credit card works the same except it is a credit card requiring repayment. he debit card funds draws down the account balance.
For merchants that use Square or Paypal the rate for Amex is the same as for any other card. Paypal offers a service to take cards in person and not just online.
I have a very small side gig where I use Square to take credit cards and I can take pretty much any form of credit card including Apple Pay and other phone payments.
Brian, same for the payments with QuickBooks...same fee across the board except for ACH which is free.
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The most expensive tool is the one you buy "cheaply" and often...
My vet refused my American Express card. I still have the card, but it is retired.
Food for thought.
nerdwallet.com/blog/credit-cards/retailers-accept-american-express/