They are touring, travelling from town to town. Putting on a concert requires all the backstage hands as well as the performers, and they have to be paid; plus the expenses of travelling, hotels, food, and the cost of the venues. They can only meet these costs if the takings (the money from the number of fans turning up and buying tickets) is greater than the expenditure. If they are just about breaking even, but then have a town where they make a big loss, then the anxiety is, will we do well in the next town and recoup our losses, or go broke (bankrupt). So, each town they go to, there is the anxiety about tickets sales, and whether they will cover their expenses or not; and hence, the fear of bankruptcy every night.