Setting blocks error help

Currently trying to set a block using the following code:

Code:

$sender->sendMessage("Making Blocks! :D");
 $x = $sender->x;
 $y = $sender->z - 1;
$z = $sender->z;
$pos = new Vector3($x, $y, $z);
 $block = 5;
$level = $sender->getLevel();
$level->setBlock($pos, $block);

currently getting this error:

Code:

[CRITICAL] Unhandled exception executing command 'blocks' in Blocks: Class FirstPlugin\Vector3 not found
20:43:13 [CRITICAL] ClassNotFoundException: "Class FirstPlugin\Vector3 not found" (EXCEPTION) in "/src/spl/BaseClassLoader" at line 122

Thanks in advance!

bump

I think the "$y = $sender->Z - 1;" needs to be this
" $y = $sender->y - 1; "