Can't claim GST in online shopping?

Hi
So all these online shopping websites send us GST invoices. As a seller you have to be GST compliant to be able to sell. But these websites, like flipkart, they don’t support B2B transaction. Hence you can’t give your GST number to claim it. Now consider I own a small shop or small business. I want to put a TV in my work place. Since I’m registered with GST, I have the right to claim it in my purchase by getting my number quoted on the bill by the seller. That way we are sure that the seller also is showing that as his sale and paying GST to the government. The customer care says they don’t support adding GST number on the invoice. Why is that? The scenario as given above, ain’t it more of a consumer buying it, but just being able to claim GST because that electronic item is an asset of his business? So why can’t we claim GST on online shopping?