Approval for the sale of sourdough to the chain

Did you ask them if they themselves also sold? It's possible that the chain organized a sale for everyone. In principle, you should ask the person who signed the certificate because they know the reality and know exactly what was there. But in general, I don't think there is any need to worry. These are crackers that are not leavened, and at most contain some mixture, so this is a question of the Rabbinic prohibition of leavened bread that has passed Passover, and it can be relaxed.