【Updated: 】
For some summoning events, you can only receive a free 5★ summon after summoning 40 times if you are a Feh Pass subscriber at the time.
Please refer to the in-app notifications for each summoning event and information about Feh Pass via the link below:
https://fehpass.fire-emblem-heroes.com/en-US/system/#no1
If this information does not help, please make an inquiry to our Support team.