Government of Ghana Treasury Bills (T-Bills) are short-term loans you make to the government. You buy them at a discount and receive the face value at maturity. The difference is your interest.
The auction calendar. The Bank of Ghana holds auctions weekly (typically Fridays), and results are published the same day. Tenors: 91-day, 182-day, 364-day.
Discount rate vs interest rate. The discount rate is the rate used to price the bill. The interest rate (yield) is what you actually earn over the holding period. For a 91-day bill, the interest rate is roughly discount / (1 - discount × 91/365). Don't worry about the formula — most platforms, including Nkosuo, show both.
Rollovers. At maturity, you can automatically reinvest (roll over) into a new bill at the new auction rate. In a falling-rate environment, your new yield will be lower; in a rising-rate environment, higher.
Where you buy them. Via a primary dealer (most banks) or a licensed broker. Some fintechs (Dalex, Bills Africa, CediRates partners) offer MoMo-native flows.