You won’t be able to top up or withdraw from a locked Simple Guaranteed portfolio for the/during the lock-in period (which is 1/3/6/12 months). Therefore, whatever amount you invest will remain fixed during the lock-in period.

Alternatively, you can always create an additional Simple Guaranteed portfolio and have multiple portfolios earning returns at the same time. At the end of the lock-in period, you’ll be able to top up or reduce your investment amount and create another Simple Guaranteed portfolio.