You can activate Amex if you have a Merchant ID from your agreement with American Express
Under Settings → Payment methods you will find all of your active payment methods. You can also activate more payment methods from here. To activate American Express, you need to enter your Amex Merchant ID into the input field and press Add American Express.
If your Amex Merchant ID was successfully submitted you will receive a success message. Your Amex support will then be active for all of your terminals since this is on a merchant level.
If you only want to add Amex to a specific store, please contact our support in the chat here, or through support@surfboardpayments.com