I tried to see if I could access the website but no luck. Are you sure what you posted is the correct website? If you don't mind, I would like to know how you got to know about the platform.
Probably something is wrong with the site because it has a domain that was created fee months ago:
https://www.whois.com/whois/idexop.vipLikely he was scammed.
If they were real and your fund is already stocked with them, they would have paid you 80% and taken 20%. Asking you to deposit more money to cover for taxes sends a red flag. If you go ahead with the deposit you will be incurring more losses to yourself because you won't be able to withdraw your funds at the end of the day. This is a scam and you should stay away.
Scammers have different ways of scamming people, a victim can pay some of them and they will not return anything and still find more ways to ask for more money.