Vivo device

Find "Forex alarm app" then turn on/allow it as instruction form Vivo global support site: https://www.vivo.com/en/support/questionByTitle?title=How%20to%20turn%20on/off%20High%20background%20power%20consumption?.

How to turn on/off High background power consumption?

For Funtouch OS 3.0 and higher version, go to Settings>Battery>High background power consumption, then you can allow or disallow apps to run in the background even though they consume much power.

For the below Funtouch OS 3.0 version, go to i Manager>Power manager>Excessive background battery usage, then you can allow or disallow apps to run in the background even though they consume much power.