Credits in Prospi are used for lead sourcing and enrichment - finding and verifying email addresses for your lead lists.
Yes, unused credits roll over to the next month. If you do not use all your credits in a given billing cycle, they carry over and are added to your next month's allocation.
Credits are deducted when you:
Enrich emails in an existing list
Import a CSV lead list
If you need more credits within a given month, you can top up your credits.