To get all items data from steam marketplace

[Growth777 BitSkins.com]

Hello! I want to have market data about all skins from one api call like though /market/priceoverview/.

I have found api named GetMarketPrices, it is look like this is do than I need. But it is not work. I am entering — https://api.steampowered.com/ISteamEconomy/GetMarketPrices/v1/?key=MY_API&appid=730

Where MY_API is my api and have error like

Forbidden
Access is denied. Retrying will not help. Please verify your
key=
parameter.

Can you help my what is the best way for my tasks?