Hi there @Subramanian, welcome aboard to the Fitbit Community! In this case keep in ind the Xiaomi Redmi 4A is not listed as compatible. In these scenarios does not mean it won't work but we cannot guarantee the behavior of the app or the tracker with the functionality of your phone.
It wouldn't hurt to try the following steps if you are not able to sync: Having trouble syncing? (here's how to fix this). If that does not work, I suggest setting up and syncing via a device listed as supported or using a computer. I know is not the best solution, but this is just a workaround while our team is always working to test and add more Android devices to the supported devices list, so keep an eye open for updates!
Hope this helps and let me know if you have other questions.
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