There are multiple legal solutions birthing various answers and not just one answer. What is best is determined by the peculiarities of the transaction, the desires of both parties, the exit strategy of the investor(s) and the expertise of the solicitors.
Instead of considering an investment as an outright loan, you can look at more robust and better options.
1. Investment for Equity. Put in X amount, get Y number of shares in the company and nominate Z number of directors on the board.
2. Hybrid Investment: The investee accepts X amount as investment sum and offers the investor Y% of the shares of the company.
The X amount acts as an hybrid loan in the sense that a percentage of Y shares vests upon the investors immediately and the remaining percentage vests on one major condition: IF the investee is unable to pay the loan after an agreed period.
3. Outright Loan: The investment works as an loan repayable by the investee to the investor at agreed terms.
You may not need to recapitalise your company to 5BN share capital. Except specific industry legislation stipulates the share capital for players on the sector, you can as well make it 10M shares of 500Naira each. It all depends on how investment-savvy your transaction solicitors are.