If you are not receiving your daily login bonus ("Test Your Luck") try fully closing the game and reopening it. Usually this can be done by double-tapping the home button on your device, but this may vary depending on your device. Once a list of open applications is shown, drag the game photo away from your screen to close it or press the close button.
If you still do not see the Test Your Luck screen, make sure your device's date/time are set correctly. Note that changing your device's date/time to anything other than the actual date/time may cause problems with receiving this reward as well as other scheduled rewards, such as Faction Wars tournament rewards. If you have adjusted your date/time on your device to incorrect dates or times while playing the game, your daily login rewards may stop working but should eventually return upon correcting your date/time settings.
You should also make sure that this is the only device you are using that is logged into WBPlay/WBID for Mortal Kombat Mobile.
If you are still experiencing issues with receiving your daily "Test Your Luck" reward, then please contact WB Games Support by clicking "Ask for Help" above.