Why my SWEP is giving error ?

[HelpMePlis]

function SWEP:PrimaryAttack()
local stalker = self.Owner
if stalker:IsPlayer() then
self:DoShootEffect()
local otherPlayer = self.Owner:GetEyeTrace().Entity
if ( IsValid( otherPlayer ) and otherPlayer:IsPlayer() ) then
if not timer.Exists( "nome" ) then
if stalker:IsPlayer() and IsValid(stalker) then
stalker:addMoney(200)
timer.Create( "nome", 5, 1, function() return false end )
end
end
end
end
end

This is the error: lua/weapons/stalker.lua:51: attempt to call method 'addMoney' (a nil value)
  1. unknown - addons/ascps2/lua/weapons/stalker.lua:51

[LearningLua]

Could be any number of things...

stalker.addMoney(200)
stalker.AddMoney(200)
stalker:AddMoney(200)

I'm assuming you're on DarkRP?

[HelpMePlis]

Yes.

[LearningLua]

are you running this code client side or server side?

[HelpMePlis]

Server side

[LearningLua]

actually quick question is the error yellow or blue in the console?

[HelpMePlis]

Yellow

[LearningLua]

Lua errors work like this:
Yellow = Client
Blue = Server

Since it's yellow that means you're trying to set the owner's money on client side but that function doesn't exist on the client's side.

Lua Tutorial 3 (If you're to lazy to look at GMod Wiki)

You would need to do an
if SERVER then
statement in the shared.lua file and (I think) you can just copy paste that code into there.