How to run pomodoro in background on iphone?

Question

iPhone

Scenario:
1. I start the pomodoro timer on Iphone
2. I lock the phone.
3. After some time, I discover that I have not heard the signal for a long time.
4. I unlock the phone, and the application was unloaded and, accordingly, did not work, the timer got stuck halfway.

How to defeat this script so that the timer runs in the background?
Locking your phone is not an option. Firstly, I don’t want to put the battery in an empty one, it will still come in handy for me.
Secondly, I can still lock it on the machine after some call.

Answer 1

Strange behavior.
On Flat Tomato (also one of the pomodoro timer applications), even if it crashes, it still counts time in the background and sends notifications to whatever it is. For the rest of the applications I will not say, I did not use them for a long period.