[New Api] Unknown problem generating flat worlds

I'm having a strange problem with flat world generation. I tried different codes but the generated world isn't flat.
Codes:

PHP:

//First code
$this->getServer()->generateLevel("test", null, "FLAT", array("2;7,2x3,2;1;"));
//Second code
$this->getServer()->generateLevel("test", null, "flat", array("2;7,2x3,2;1;"));
//Third code
$this->getServer()->generateLevel("test", null, "pocketmine//level//generator//Flat", array("2;7,2x3,2;1;"));
//...


I tried also without double slashes but the world isn't flat

I have the same problem!

You need to key the preset string "preset".
array("preset" => "...")

An example?

It is already an example... :facepalm:

I did it but It still doesn't work. Codes:

PHP:

//First code
$this->getServer()->generateLevel("test", null, "FLAT", array("preset" => "2;7,2x3,2;1;"));
//Second code
$this->getServer()->generateLevel("test", null, "flat", array("preset" => "2;7,2x3,2;1;"));
//Third code
$this->getServer()->generateLevel("test", null, "pocketmine//level//generator//Flat", array("preset" => "2;7,2x3,2;1;"));
//...

What did I do wrong?