Because of copyright and legal complexities, the key is not bundled directly with the manager. Users typically find it on community modding hubs like FiferMods or Soccer Gaming . How to Set Up Frosty Mod Manager for FIFA 19

is a legitimate, free tool used to apply mods to PC versions of FIFA games (including FIFA 19). It does not require a "key" to function. If you've seen websites selling or requesting a "key" for Frosty Mod Manager, these are likely scams attempting to monetize free software, or they could be distributing malware.

You do not need a key. If the software is asking for one, you have downloaded the wrong file. Head to Nexus Mods, download the latest Alpha build of Frosty Mod Manager, ensure your FIFA 19 game path is correct, and ensure you are running the tool as an Administrator.