If your account currently has a negative balance of Contest Credits, you will be unable to use the gifting feature in the game until you have returned your Contest Credit balance to zero. No purchases of Contest Credits will include any bonus or event items. However, once you have repaid the negative balance in full, you can access the gifting feature if it is still active and make Unit purchases again.
For more information on paying off your negative balance, please refer to our article on Negative Red Units here.