Why is the Square option grayed out?

Hello, I want to integrate square for payment but it is grayed out. Only paypal is available. How do I incorporate it into the form?

Please note that you can add only one payment field in one form. That is why other options are grayed out since the PayPal Standard payment is integrated into the form. 

If you want to add Square, you will need to delete the PayPal Standard payment field first and then add Square payment. 

After you delete the PayPal Standard payment, you will be able to see that none of the payment fields under the Payments tab will be grayed out. Now select "Square" from the Payments tab and add it into your form.