Prestashop fatal error on On Sale Module -

i downloaded module roja45: on sale products, it's free , easy find on google.

after installation have problem seeing on sale on 1 page.

first showing error controller changed name of from: roja45onsaleproducts.php to: roja45onsaleproducts.php , error apeared.

in debug see error:

fatal error: call private method roja45onsaleproducts::getproductstodisplay() context 'roja45onsaleproductsroja45onsaleproductsmodulefrontcontroller' in /home/psdes/domains/dev/moto-center/modules/roja45onsaleproducts/controllers/front/roja45onsaleproducts.php on line 68

and line 68 in error is:

$products = roja45onsaleproducts::$cache_onsale_products; if ($products === null) {     $products = roja45onsaleproducts::getonsaleproducts((int) $this->context->language->id, 0, (int) configuration::get('ps_roja45_onsale_products_nbr')); } 

line 68 just:

$products = roja45onsaleproducts::getonsaleproducts((int) $this->context->language->id, 0, (int) configuration::get('ps_roja45_onsale_products_nbr')); 

can take wrong?

i can't information module developer.

in module file roja45onsaleproducts.php change private function getonsaleproducts(...) public function getonsaleproducts(...).