Calling a flow through REST api returns "http body is required" error

Question

I'm trying to initiate a flow through the REST api using PHP:

$url = "https://myInstance.salesforce.com/services/data/v40.0/actions/custom/flow/EndCourse_and_Semester_Notification";

$headers = array(
    "Authorization: OAuth myAccessToken",
    "Content-type: application/json",
    "Content-Length: 0"
);

$body = '{}';

$curl = curl_init($url);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $body);
$response = curl_exec($curl);

var_dump($response;
curl_close($curl);

(myInstance replaces my instace and the same goes for the access token)

When i print the response i get the following error message:

string(118) "[{"message":"The HTTP entity body is required, but this request has no entity body.","errorCode":"JSON_PARSER_ERROR"}]"

Why is this happening? i have an empty body and a size defined. Also worth mentioning is that i tried doing the same without a body or size defined and then i got an error of:

"POST requires content-length"

Answer 1

flow expect input parameters while calling through API so you need to pass blank input array if you are not passing any value. Update your body with following json

{
"inputs": [
    {}
 ]
}

So your code will look like this

$url = "https://myInstance.salesforce.com/services/data/v40.0/actions/custom/flow/EndCourse_and_Semester_Notification";

$headers = array(
    "Authorization: OAuth myAccessToken",
    "Content-type: application/json",
    "Content-Length: 0"
);

$body = '{"inputs":[{}]}';

$curl = curl_init($url);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $body);
$response = curl_exec($curl);

var_dump($response;
curl_close($curl);