"Not enough credits"
What the dialog is telling you and what to do.
The generation would cost more than your balance. The dialog shows the price, your balance and the shortfall.
- On a paid plan: top up, or make the clip shorter, or drop to a cheaper model or route.
- On the Free plan: credits cannot be bought, so either wait, use a cheaper route, or move to a paid plan.
The cheapest meaningful change is usually the model, then the length, then the route — in that order.