How do i get Credit and what are the differences between member groups?

When I need a m2 theme, I search Google and find this site, and I will buy some credit to download some extensions from this site, because it's cheaper than a site I once clicked.
 
I have purchased 10 credits to download one resource. But the download link are down, and no more valid. Now when I am again trying to download the resource, then I am getting the message that I need to buy credit again. May I know if this is usual behaviour or there is any issue in website?

Update - Got the new download link in private DM. Sorted now.
 
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