php - Understanding PayPal's REST API -

Our group of people I work with requires easy invoicing system for our customers. Each of us has our own PayPal account.

We want to be able to generate invoices, where the invoice will link to the person's PayPal account, which generated it. So, for example, the invoice can have a PayPal button that links the paypal to the customer if I had to generate an invoice, then that paypal button will join me so that I get the money. If my colleague prepares the invoice, the PayPal button should be linked to him / her so that he can get the money. Finally, we should also be able to retrieve the invoicing status (paid / unpaid).

I've been reading PayPal's API again and again, and I still do not understand how I can do something like this work to authenticate each of us with PayPal's Need to generate your API key through?

I downloaded a script that works, where it does not ask me for any API key or password or password. It asks me for my PayPal email address, and somehow it works. It is also able to retrieve payment status. Can anyone give me advice about this work?

EDIT: I have an IPN listener in the script downloaded, but I am still confused about how he can get PayPal payment status from my PayPal email address.

There are a few options for an app like this

1) Create as a service provider, where you will use a set of API credentials (the owner of the app) and after that your API will be the user with System Grant API permissions for making the API the user calls himself You can do this manually from the account or you have the permissions API You can use it.

2) Create an app with a setting panel where people can copy / paste their API credentials into their user profiles / settings. Page. You can then use those API credentials in the API request.

The invoicing API will be an instrument that you are using to make real invoices, of course, and then the IPN will actually be what you do automatically update your system when paying an invoice (Or is updated in any way.)

PayPal will return a "PayPal invoice ID" and you can also pass in your own invoice ID if you have your own Istm is paid invoices which two will be returned to the Aipian, you can update accordingly to your system.