OK, I’ll stop being annoying and just explain it 
: ‘self’ is always given as a function argument. In other words, a local variable inside a function. The problem is, you are not passing ‘self’ on to the “generate_book_code()” function, so ‘self’ doesn’t exist inside that function when it runs. You want to do this:
function init(self)
generate_book_appearance(self)
generate_book_code(self)
end
local function generate_book_code(self)
self.book_code = ""
HOLY CRAP, I FEEL DUMB. Also I was having dinner and that popped into my head, I was thinking about how I had arguments inside of insert-book-code.script and they all passed self. THAT MAKES SENSE NOW. 
Wait though, would I even need to make the variables inside of book.script unique? Considering I’m using the factory to make a unique instance each time?
Thanks by the way for sticking it out with me.
Ok, I’m making progress though, managed to fix another error, it was the msg.post one, I was passing a string instead of a table and it didn’t like that, and I fixed it, still got a few errors to go though.
ERROR:GAMEOBJECT: Component '/instance0#random_book_code_label' could not be found when dispatching message 'set_text' sent from default:/instance0#random-book
ERROR:GAMEOBJECT: Instance '<unknown>' could not be found when dispatching message 'play_sound' sent from default:/minigame_go#insert-book-code
INFO:DLIB: SSDP: Started on address 10.0.0.78
ERROR:SCRIPT: ...games/inventory/insert-book-code/insert-book-code.script:25: Could not send message 'game_over' from 'default:/minigame_go#insert-book-code' to 'main:/main'.
stack traceback:
[C]:-1: in function post
...games/inventory/insert-book-code/insert-book-code.script:25: in function <...games/inventory/insert-book-code/insert-book-code.script:24>
Ah ok, I’d probably have to pass in that instance for the url then.
local function generate_book_code(self)
self.book_code = ""
local charset = {} do
-- Ký tự [0-9a-zA-Z] dưới dạng mã ASCII: https://www.rapidtables.com/code/text/ascii-table.html
for c = 48, 57 do table.insert(charset, string.char(c)) end
for c = 65, 90 do table.insert(charset, string.char(c)) end
for c = 97, 122 do table.insert(charset, string.char(c)) end
end
-- [0-9a-zA-Z]{4}-[0-9a-zA-Z]{4}-[0-9a-zA-Z]{4}-[0-9a-zA-Z]{4}
while (string.len(self.book_code) <= 19) do
if (#self.book_code % 5 == 0) then
self.book_code = self.book_code .."-"
else
self.book_code = self.book_code .. charset[math.random(1, #charset)]
end
end
-- Ok, this is the issue here. I already tried to pass self"#random_book_code_label" but that didn't work
label.set_text("#random_book_code_label", self.book_code)
msg.post("/computer#computer", "actual_book_code", {book_code = self.book_code})
end
Wait nope, fixed that issue too, turns out I got the wrong name for the label. 
There’s still the play_sound issue, will try to figure that out, in fact I’m trying to find where it is. Got the sound to work. Gotta figure out how to make my spawned game object bigger, I’ll figure that out, I think you can specify scale with factory. Unless there’s a way to do that in the game object itself. Another one is to figure out how to check to see if your typed input matches the book code, hm. Oh yea, and trying to figure out how to return to the main collection and then loading the next minigame. We’ll get to that when we get to that.
Alright, it sort of works, just one odd problem now, with the timer, after it’s done it’s giving me an error where it can’t find the main collection.
What is the code you are running in the timer?
// timer
timer.delay(1, false, function()
msg.post("main:/main#main", "game_over")
end)
// main
function on_message(self, message_id, message, sender)
if message_id == hash("game_over") then
pprint("Create nested function for loading and unloading minigames?")
end
end
ERROR:SCRIPT: ...games/inventory/insert-book-code/insert-book-code.script:24: Could not send message 'game_over' from 'default:/minigame_go#insert-book-code' to 'main:/main#main'.
stack traceback:
I wonder if it has to do with the directory.
No no no. The way you have arranged stuff in your Assets (the panel on the left) in terms of filenames and folder structure has nothing to do with the url used in msg.post. It is the structure in the Outline that matter, and the ids you have assigned there.
if message_id == hash("proxy_unloaded") then
pprint("Cycle through the minigames again.")
end
Hate to revive a thread, solved one scenario but now have a similar scenario to this one. Basically I’m now trying to spawn a bunch of game objects that have a different sprite for each instance (basically they’re just alphabetical letters) and am using Factory and Properties as an example, however I don’t think I need to add functionality to the game object I’m spawning in its own script since it’s just being used in this specific collection. I would assume that me using self.letter would make each instance unique, so I don’t understand why it wouldn’t recognise the id, and since self.letter is an instance of the spawned game object, shouldn’t go.animate recognise that path? Thanks to anyone who responds.
local function random_position()
return vmath.vector3(math.random(1, sys.get_config("display.width")), math.random(1, sys.get_config("display.height")), 0)
end
local function spawn_letters(self)
local charset = {} do
-- Ký tự [0-9a-zA-Z] dưới dạng mã ASCII: https://www.rapidtables.com/code/text/ascii-table.html
for c = 97, 122 do table.insert(charset, string.char(c)) end
end
for i,v in ipairs(charset) do
self.letter = factory.create("#alphabet_factory", random_position())
sprite.play_flipbook(self.letter.."#alphabet_sprite","keyboard_"..v)
go.animate(self.letter.."#alphabet_sprite", "tint", go.PLAYBACK_LOOP_PINGPONG, self.color, go.EASING_INOUTCIRC, 2)
end
end
function init(self)
msg.post(".", "acquire_input_focus")
spawn_letters(self)
timer.delay(8, false, function()
print("Failed.")
msg.post("main:/main#main", "game_over", {score = 0})
end)
end
function on_input(self, action_id, action)
end
function final(self)
msg.post(".", "release_input_focus")
end
Errors below:
ERROR:SCRIPT: ...est-service/where-to-find-book/where_to_find_book.script:14: Could not find any instance with id '<unknown>'.
stack traceback:
[C]:-1: in function animate
...est-service/where-to-find-book/where_to_find_book.script:14: in function spawn_letters
...est-service/where-to-find-book/where_to_find_book.script:20: in function <...est-service/where-to-find-book/where_to_find_book.script:18>
You can’t use string concatenation. Use:
msg.url(nil, self.letter, “alphabet_sprite”)
Thanks for replying britzl, but how would I determine what image the sprite should be set to?
Is this not what you are looking for as Britzl suggested?
local sprite_url = msg.url(nil, self.letter, “alphabet_sprite”)
sprite.play_flipbook(sprite_url,"keyboard_"..v)
Ah I see, yea I realise I made a typo on my variable name (and now I feel dumb). 
Thanks selimanac for replying.
I guess the problem is the animating part now.
ERROR:GAMEOBJECT: Properties can not be of type 'nil'.
ERROR:SCRIPT: ...est-service/where-to-find-book/where_to_find_book.script:14: only numerical values can be used as target values for animation
stack traceback:
[C]:-1: in function animate
...est-service/where-to-find-book/where_to_find_book.script:14: in function spawn_letters
...est-service/where-to-find-book/where_to_find_book.script:20: in function <...est-service/where-to-find-book/where_to_find_book.script:18>
pprint(self.color)
Ah I see, it’s a nil value, ok, I see now, I should’ve been animating the position property, not the color, that was my bad. It’s working now mostly. Tried bumping up the speed of the animation but it seems like they’re still not moving. Hm, shouldn’t it move though? I called random_position() twice. Just debugged it, yea random_position() works.
go.animate(self.letter, "position", go.PLAYBACK_LOOP_PINGPONG, random_position(), go.EASING_INOUTCIRC, math.random(1200, 2400))
Your URL works, random_position() works. So, what might be the problem?
Are you sure this duration is proper?
Did you try something like 1 or 2 for duration?
Are you sure the start position and end position is different or distance between them large enough for duration 1200-2400?
math.random(1200, 2400)
Thank you for pointing that out, no it wouldn’t actually make sense for it to be that big logically speaking. So I changed it to 1-10 instead, which is a lot better now, I still have to figure out how to make it not go offscreen, I wonder if it has to do with the fact I’m using rendercam so I’d have to translate from screen view to world view like with inputs. I think in the random_position method I’d have to tweak it so it converts from screen to world view.
I’m looking at the rendercam scripts and I don’t see a method like GetViewportSize(), I’ll see if I can look into it more. There’s a set_viewport() but I’m not sure if that’s what I’m looking for.
Also I just realised it’s theoretically possible to randomly generate a position and have a chance it be the same position twice, I’d probably have to make a method that checks to make sure that’s not the case and if it is, then rerandomise it.
If I do something like this,
local screen = vmath.vector3(action.x, action.y, 0)
wouldn’t it be grabbing the location of the cursor, i.e. action.x, action.y? That wouldn’t be the viewport size though.
Just going to use default camera since I’m not using orthogonal or perspective view.