Identify the source document for each of the following transactions: Goods returned by debtor, Payment received from debtor, Charge debtor interest, Send stock back to creditor.

Here are the source documents for the given transactions:

3.1.1 Goods returned to the business from a debtor.
The source document is a Credit Note.
$\boxed{\text{Credit Note}}$

3.1.2 Payment received from a debtor.
The source document is a Receipt.
$\boxed{\text{Receipt}}$

3.1.3 Charge a debtor interest on his overdue account.
The source document is a Debit Note.
$\boxed{\text{Debit Note}}$

3.1.4 Send stock back to the creditor.
The source document is a Debit Note.
$\boxed{\text{Debit Note}}$