Money - see also laundering.
We already know one possible way this has been funded - Clem is being chased through the court systems of the UK and Australia by creditors of his closed businesses with claims including the fact he moved money owed to them into the football club, having liquidated at least two businesses to avoid paying them. That is their claim, not mine.
We also know we have one current Agent heavily involved in the clubs transfer business - it is clear how that makes that individual money. An ex-agent's business still involved and having waved the sale to a new owner through when they were using the Courts to chase after several million from the club/previous owner. Didn't look like the sort of person who would suddenly walk away without some future promises.
We had one "Consultant" essentially employing the DoF Operations and subsequently loaning the owner money and sort of becoming a Director in Kiely. I can imagine he has charged the club money for those services.
We have someone setting up an "Academy" in Pakistan with a funded Scholarship, using STFC as the sponsoring company, with the obvious intent of using the Visa system to charge for entry. The area in question is also prone to money exchanging hands off the books.
While I am dubious about Clem putting that much of "his" money in, I don't think his pay off has come yet. I think he was convinced to takeover by the motley crew, believing he could make money either through the ground development (given ownership was going to be gifted) or longer term by using it as a prototype to show off to prospective customers.
Just look at the history as well, we have someone who was paying for a lease on some land for a car wash (a business often used for different sorts of washing) and as far as I can tell, having never actually even bothered to wash a car? We have an ex-most wanted who is involved in a dodgy sports business who is kind of in charge of conditioning and "found" a few youth prospects to funnel to the club. And so on. Nobody is making billions, but plenty can make enough to carry the whole thing on for as long as they can squeeze it.