Paypal in-app donation using Titanium

Question

I'm implementing a Paypal donation button in a charity app. I'm getting really (but really) confused from the tons of misleading informations and notions provided by Paypal's documentation. I'm looking for someone that can explain me what I need (and eventualy what I don't) to accomplish this task:

A donation button in a view. When the user tap on it, it appears the Paypal's login form. if the user authenticates properly, money are transferred directly on the charity organization's account, otherway an errow is thrown

Here you can find the example provided by the authors of Titanium Paypal plugin, in which a button it's correctly instantiated and injected into the GUI. I guess that's the proper implementation I need (is it?) In there, there're some concepts I miss:

1. appID - do I need one? Being this a not-advanced transation, it shouldn't be necessary, but...
2. recipient - should be the user for the charity organization account or, better said, the user given as Classic API username for the charity organizzation account. Is just specifying this is enough for addressing the transaction through their Paypal account?
3. API Password, API Signature - it seems they play no role in this transaction, isn't it?
4. SandBox - I know I can create fake users with a fake wallet. Then they can login in my app (as it's in PAYPAL_ENV_SANDBOX status) and perform fake operations. Am I missing something?

I used the code above, but results are not satisfying I can't never login as a user for paying.

Can anyone provide me a brief explanation of what I have to do?

Thanks

EDIT 01/21/2014

thanks to @andrew-angell I set my mind clear about above concepts, but I'm still freaking-out with the Titanium plugin you find in the GitHub's link above. In there, it seems there's no place to insert API credentials. Moreover, I'm still getting the "Unexpected error, code -1" if I try to use the button in SANDBOX environment (but it works in NONE environment). Docs and Examples are so straightforward that make me feel stupid for not getting them work. I'll continue development in demo mode (NONE environment), but I wish I could do it in SANDBOX.

Answer 1

1. If the SDK you're using is using Adaptive Payments (which it looks like it must be if it's calling for an App ID) then yes, you will need that in order to make live calls.

2. If you want the money to fall into 3rd party PayPal accounts you'll need to set them as the receiver in your payment and you'll need to utilize Preapproval profiles or Permissions to allow payer's to configure your app so it can make payments on their behalf.

3. You will always need your API username, password, and signature when working with the classic API's.

4. Yes, the sandbox is for testing your application without spending real money.

When you say the results are not satisfying, what exactly is going wrong?