WP functions in custom functions

I’m having problems calling WordPress functions in my custom in functions. In short, they don’t work…

Here’s what I’m trying to do:

function getMetadata($keyToPlayin) {
	global $post;
	if (get_post_meta($post->ID, '$keyToPlayin', true)) {
		echo "working!!!";
	};
}
getMetadata(client)

It works fine when I take it out of the function.
And I can grab the post ID, but get_post_meta() never runs… Sorry, I’m PHP n00b here.