Thank you for reaching out to the Community! I'm happy to provide some assistance with selecting a card reader, to ensure this gets resolved.
To share some insight, external card readers can certainly be used to sell in-person with the POS. It does however, have some limitations including removing your ability to use Shopify Payments. We have a great Card Readers document that touches on these limitations in further detail, that I recommend checking out.
Additionally, you will need to determine what card types your payment processor accepts and set up an account with them. To learn more about this, you can check out our Using External Card Readers document as it touches on this further.
Please let me know if you have any other questions or concerns.
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