A campaign that runs out of wallet balance pauses and later continues from the same recipient, so nothing is ever lost. But you found out only when the campaign stopped halfway.

The campaign page now tells you first. If the wallet cannot pay for every recipient, it says about where the campaign will stop, and how much you need to add to finish it.

It is a warning, not a block. You can top up while a campaign runs, and the campaign continues from where it paused. Read more in the billing and wallet guide.