Credits are held while something generates and settled when it finishes. Nothing is ever deducted before you see the price, and a failure releases the hold in full.
Every paid action shows its cost, your balance before, and your balance after — before it runs.
Generation costs credits. Reading, editing, copying, exporting and sharing your own work do not — not now, not on any plan.
Your monthly allowance is used first, then pack credits. Pack credits never expire; monthly allowance does not roll over. Downgrading a plan keeps every pack credit you have bought.