CURLOPT_POSTFIELDS by default accepts strings and flat (1-dimensional) arrays.
Update payload validation of Curl->sendRequest method to allow arrays or let user to set payload manually using curl options (do not set payload if it is empty).
Without that it's impossible to post files.
$payload['file'] = new \CURLFile($file, $mimeType);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
CURLOPT_POSTFIELDS by default accepts strings and flat (1-dimensional) arrays.
Update payload validation of Curl->sendRequest method to allow arrays or let user to set payload manually using curl options (do not set payload if it is empty).
Without that it's impossible to post files.
$payload['file'] = new \CURLFile($file, $mimeType);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);