If you are making the donation, you must pay the full donation upon approval of your citizenship. You will only be granted citizenship once the donation or the investment in property is completed. If purchasing real estate, it depends on the property you purchase. If you are buying a share of a property (generally all that you can do at the minimum investment level of 200,000 USD) then the share must be paid for in full upon closing. If you are purchasing a villa to be built, you will likely have to pay for the land upon approval and the construction payments over a 12-month period whilst the property is built. Bear in mind too that the citizenship by investment unit will want to see proof of available funds in your financial or bank statements that you can close on the property or make the donation upon approval i.e. generally they want to see the cash in the bank when you make the application.
