@Meri417 I think that 1 promotion available indicates that there is only one time period identified by AirBnB as promotable that you have not taken as an opportunity. I.e., all other time periods are already promoted.
To my knowledge, there is no limit on how many promotions you can run, but I do have a question. If you are running all available promotions to get a higher booking percentage, might you need to look over your overall pricing strategy? It sounds like you are always offering a discount…much like Walmart.