@Burak-Belezoglu
Hi there,
Once a Fantasy League has been created, all managers that want to join it will have to create their team within the first hour of acceptance. So you probably didn't created your team within the hour.
I don't know if the league will start now, but you won't be able to join that league now. The best thing you can do is go to our support. They can check this and if needed delete the league. That way you can create a new Fantasy League.
You can find our support through the below link.
https://support.onlinesoccermanager.com/hc/en-us
Then click on 'submit a request' and choose the option 'OSM' from the dropdown menu to fill in the contact form.