A: This depends on the Product you've activated. You don't need credits with Company Data Hub, but you do with Bisnode.
Company Data Hub: each matched company uses Company Data Hub tokens, which count towards your Company Data Hub price tier. You can see your usage as Used CDH tokens in Settings → Account → Billing portal. If you use Update all companies and the matches would take you past your current tier, Upsales matches as many companies as fit within the tier and creates a Request to upgrade tier in the Billing portal. When the request is approved, the remaining companies are matched. Companies you match one by one in Match companies are always matched and their tokens are added to your usage.
Bisnode: each matched company uses one Bisnode credit. If you don't have enough credits for the companies you match, nothing is matched. You buy more credits in the Billing portal.