You may be holding an unlisted asset/fund that is not like a regular unitised structure. Rather it is to be recorded as a value of investment.
In the case where a fund is not unit-based you would still enter the transaction as a buy within 'Other Assets'
You would then enter the number of units purchased as 1 and price as the value of the purchase.
Then periodically in the Value History you will update the value per unit as the total current value.