Timer app which works in background mode

I am developing multi timer app which works in background mode. at first, I could go multi timer in background mode using background mode 'audio' which uses slient wav file. However, app has rejected background mode 'audio' should not use which not for audio app. I want to know how to develop timer app which works in background mode in ios platform. native ios timer that let us alarmed time. so I want develop that kind of app Sincerely,

Timer app which works in background mode
 
 
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