Apologies for any confusion, as you probably know there are fund and provider fees for every investing platform which is usually in the form of %. With Plum specifically these are:
The Fund. The Fund providers, Vanguard and others (specified on each fund page), have a team working every day to buy and sell stocks aiming to ensure the fund achieves its objectives. They charge an annual fund management fee for this. It is a percentage fee which differs per fund (e.g. Basic funds carry a 0.22% fee). This is reflected in the value of the fund.
The Product Provider. To make investing possible we are working with a regulated product provider (Gaudi Regulated Services LTD), who ensures safe-keeping of your investments, and the buying and selling of funds. They make sure your ISA is declared with HMRC, and your GIA has all your investments in it. The product provider charges a percentage annual fee of 0.15% charged monthly. This is reflected in the value of the fund in your overview.
Most other providers also charge their own fee on top of these in the form of a % whereas ours are a fixed fee.
Hope that clears things up a little!