Ticket prices heavily affect match attendance and the number of fans that will visit your stadium. If the price is too high for the competition in question, your fans will not show up and that can affect your moral bonus during the live match. However, if the price is too low, your revenue will suffer.
It is your challenge as a manager to find the right balance. Try out different prices and see which one is the optimal.
You can change these settings via the Club - Finances Menu. Simply swipe to the “Ticket” tab and click on the competition that you would like to make changes for.