Make 1 API call Use API: {{Api Root}}/api/Invoices/Payment For the {{Api Root}} variable: Production: 
https://api.revolv3.com
Sandbox: 
https://api-sandbox.revolv3.com
This is a POST request with a sample payload below. This call is also in the API docs. Additional calls around payments can also be found in the docs. 
{
	"FirstName": "John",
	"LastName": "Smith",
	"MerchantCustomerRefId": "",
	"EntityUseCode": null,
	"PaymentMethod": {
		"BillingAddress": {
                    "AddressLine1": "381 Forest Ave. Suite C",
                    "City": "Laguna Beach",
                    "State": "CA",
                    "PostalCode": "92651",
                    "Country": "USA"
                },
		"BillingFirstName": "John",
		"BillingLastName": "Smith",
        "creditCard": {
            "paymentAccountNumber": "123456789123456",
            "expirationDate": "0127",
            "securityCode": "123"
        }
	},
	"Invoice": {
		"MerchantInvoiceRefId": "",
		"EntityUseCode": null,
		"InvoiceLineItems": [
			{
				"InvoiceLineItemId": 0,
				"Name": "One Time Charge",
				"Description": "Value for 600.00 dollars",
				"Value": 600.00,
				"ValueType": "Standard",
				"TaxCode": null
			}
		]
	}
}
The response from this would be 
{
    "customerId": 64,
    "invoiceId": 991,
    "merchantInvoiceRefId": "",
    "invoiceStatus": "Paid",
    "invoiceAttemptStatus": "Success",
    "message": "Authorised",
    "subtotal": 600.00,
    "taxAmount": 0.0,
    "total": 600.00,
    "paymentMethodId": 585
}