I haven't receive a report about being unable to see the Credit button after installing your PIN PAD machine.
Let's make sure the machine is properly installed and should be compatible with your POS. I also suggest checking all set up for credit card payment is selected on your settings.
Go to File, select Preferences, then Company.
Under Sales, select ReceiptTendering.
Mark the CreditCard option on the PaymentMethod section.
If still not seeing the Credit button, I recommend contacting our QuickBooks POS Technical Team. By doing so, they'll be able to check your set up to accept credit card payment. You can go to this link for the Point of Sale contact information: https://community.intuit.com/browse/payments-contact-us.