The investment can be made in several forms.
The first option is mandatory in most cases: you actually have to pay the state to get a passport. However, this fee will not be returned to you.
After that, other formats are open before you.
In some cases, you will be able to obtain residency for a charitable donation, which you also will not be able to get back.
Alternatively, you can invest the same amount in bonds
Government bonds will be less risky, but also less profitable. Corporate bonds, on the other hand, can bring in more if the company is successful on the stock market, but you can also lose some of the money with the same probability.
The same rules apply to investment funds, which also require you to figure out which areas are best to invest in.