Before you are assigned an LTC address, you need to enable a Litecoin wallet on your account.
You can do this via the Settings -> My Wallets page.
Simply tap the '+' symbol next to LTC, and tap "Confirm" to permanently enable it on your account.
Note: LTC wallets are still in early-stage production release and may be taken offline unexpectedly for maintenance. LTC Maintenance will only restrict the deposit/withdrawal functionality of LTC wallets, and any funds already in your account will not be affected.