Question: Maplets, proc calling button and autoupdate a textfield

So currently i am trying to programm a game. for that i would need a Textbox that is updating once the player makes an input. I have a textbox TB1 and a button with the action linked. the action that the button should make is calling an external procedure which in turn updates the textbox. But i currently i keep getting the following error expresion:

Error, (in Maplets:-Tools:-Set) invalid argument(s): [TB1]::string = [7, 8, 9]

So what die i do wrong.

I think you will need more information on the current way i programmed the whole thing. that is why i wrote a mock programm that should ilustrate the setup in the normal bigger file nicely.

As for the game it will be a blackjack once it is done. the rest is hopefully explained in the mock programm. plese tell me what i need to do, while i have experience in programming i do not know anything about maplets. and did not find a site that explains my problem. what i did up until now i pieced together from various sources.

Here is the programm

mockprog.mws

I am sorry if this seems like an easy question to you and greatly apreciate every moment you spend on reading this and answering

thank you and regards