Need to Fix Merchant Center Issues

I am running google shopping ads over my website and [login to view URL] and content api has been integrated over the website to transfer feeds of products directly in merchant center and then we run shopping ads for these products. But in merchant center many of my products remain disapproved and the reason mentioned by merchant center is "Mobile Landing page is unavailable 5XX error" when my site is responsive and works fine over mobile. I need someone to fix this issue of mobile device for my website so my items do not get disapproved over in merchant center.