Am I obligated to pay the gymnasium fees for the days I trained, knowing that the coach did not ask me to pay despite his awareness that I had not settled the past days?

The rule in this matter is the contract between the two parties, as Allah Almighty says: "O you who have believed, fulfill [all] contracts," and the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." As long as you know that the subscription does not entail compensation for absence, you must inquire from the owner of the hall. If he absolves you, then there is nothing upon you; otherwise, you are obliged to pay his fee. For benefits are lost by the choice of the renter, and the rent becomes due upon him even if he does not benefit.