If you buy bait, you get 5 instead of one item.

You need the Unity Mod Manager from here:
https://www.nexusmods.com/site/mods/21

Then install my mod from here:
https://www.nexusmods.com/ultimatefishingsimulator/mods/2

Start the game and make sure the mod is "green" (enabled).

p.s. Not sure, but I guess it is best to have the game installed into: C:\GOG Games\

pps. before you update the game, open Unity Mod Manager and uninstall -> update the game -> install