If you are using Gmail app not working then ensure sync Gmail is on. One that will make sure that you can’t use Gmail properly is sync Gmail option. Proceed ahead and check the settings. For this, start by opening Gmail application and from top-left corner, click on three-line menu button. Proceed to settings and choose your account. Scroll down and find the data usage section. Lastly, ensure the checkmark next to sync Gmail is toggles on. These are the steps that users need to follow to resolve the issue of Gmail application not working.