DEAR needs to have the ability to add non-integrated payment types, like AMEX. Vend does this quite nicely, see details and video below.
Non-Integrated/Manual Card Payments in Vend
Non-integrated card payments require you to type the payment amount into the card terminal and confirm in Vend that the payment is accepted to close the sale.
Using Vend, you can use any credit card/EFTPOS card payment terminal as a non-integrated stand-alone terminal. To use this, create a button for the payment type by going to Setup -> Payment Types and selecting Add Payment Type.
Tip: You can even create more than one payment button for each payment type, for example, Credit Card - Visa, Credit Card - AMEX, Credit Card - Mastercard.
Once you've chosen and named your new payment type click Save Payment Type. A button will now appear for this payment type on the payment screen the next time you process a sale. You will then need to separately set up your card payment terminal using the directions that came with the terminal.
When the time comes to take payment, you can process the payment using the terminal and hit the corresponding payment button in Vend.
Video link: https://support.vendhq.com/hc/en-us/articles/201378960-Payments-Setup
Please let us know any further information you need to implement this.