Andrew, this is highly unlikely to be implemented. There's no way invoices and payments should be removed once posted to the accounts.

That functionality isn't available in the main Sage 200 product, and the API only gives access to a subset of Sage 200's functionality.

However, if you want to suggest new features, the Idea's forum is the place to go!

What about Customers?
For instance, I create a Customer and his balance is 0$.
Then I remove this Customer.
Is it possible to receive via API this removed Customer?

Regards,
Andrew

Oh I think I see what you're trying to do - keep an external list of customers and remove records from your list if they're removed in Sage. The answer's probably no, the API will never be able to give you any data that's been deleted from Sage! 

It's rare to delete customers from Sage, much more usual to make them Hidden. But I suppose you could get a list of all customers and compare it.