MALFORMED_REQUEST trying to communicate with paypal - php

Question

I'm having trouble just sending my first API call to PayPal.
I'm hoping its just simple syntax that I got wrong.
The error I'm getting:
"name":"MALFORMED_REQUEST","message":"Incoming JSON request does not map to API request
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api.sandbox.paypal.com/v1/oauth2/token");
curl_setopt($ch, CURLOPT_HEADER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_USERPWD, $clientId.":".$secret);
curl_setopt($ch, CURLOPT_POSTFIELDS, "grant_type=client_credentials");
$result = curl_exec($ch);
if(empty($result))die("Error: No response.");
else
{
$json = json_decode($result);
$sAccessToken = $json->access_token;
$sTokenType = $json->token_type;
$sAppID = $json->app_id;
print_r($json);
}
curl_close($ch);
$ch2 = curl_init();
//curl -v https://api.sandbox.paypal.com/v1/payments/payment
curl_setopt($ch2, CURLOPT_URL, "https://api.sandbox.paypal.com/v1/payments/payment");
//-H "Content-Type:application/json" \
//-H "Authorization: Bearer <Access-Token>" \
curl_setopt($ch2, CURLOPT_HTTPHEADER, array(
"Content-Type:application/json",
"Authorization: Bearer ".$sAccessToken,
));
$payer = array(
'payment_method' => 'credit_card',
'funding_instruments' => array(
'credit_card' => array(
'number' => "4417119669820331",
"type" => "visa",
"expire_month" => "11",
"expire_year" => "2018",
"cvv2" => "874",
"first_name" => "Betsy",
"last_name" => "Buyer",
"billing_address" => array(
"line1" => "111 First Street",
"city" => "Saratoga",
"state" => "CA",
"postal_code" => "95070",
"country_code" => "US"
),
),
),
);
$params = array(
'intent' => 'sale',
'payer' => $payer,
'transactions' => array(array(
"amount" =>"7.47",
"currency" =>"USD",
"details" => array(
"subtotal"=>"7.41",
"tax"=>"0.03",
"shipping"=>"0.03"
),
"description" => "This is the payment transaction description."
)
));
curl_setopt($ch2, CURLOPT_POST, true );
curl_setopt($ch2, CURLOPT_POSTFIELDS, json_encode( $params ) );
curl_setopt($ch2, CURLOPT_SSL_VERIFYHOST, false );
curl_setopt($ch2, CURLOPT_SSL_VERIFYPEER, false );
curl_setopt($ch2, CURLOPT_RETURNTRANSFER, true );
$response2 = curl_exec( $ch2 );
$errrors2 = curl_error($ch2);
print_r($response2." / ");
print_r($errrors2);
curl_close($ch2);