wp_remote_post using x-www-form-urlencoded

functions.php

function request_token() {

		$encoded_auth  	= base64_encode( $this->client_id . ":" . $this->client_secret );
		$args  			= array(
			'method' => 'POST',
			'httpversion' => '1.1',
    		'headers'  => array(
				'Authorization' => 'Basic '. $encoded_auth,
        		'Content-Type' => 'application/x-www-form-urlencoded;charset=UTF-8',
    		),
			'body' => 'grant_type=client_credentials',
		);

		$response 	= wp_remote_post( $this->api_url, $args );
		
		// If the status code is not 200, throw an error with the raw response body
		if ( isset( $response['response'] ) && $response['response']['code'] !== 200 ) {
			throw new RuntimeException( $response['response']['message'] );
		}

		$token_response 	= json_decode( $response['body'] );

		if( isset( $token_response->error ) ){
			throw new RuntimeException( $token_response->error );
		}

		return $token_response;
	}