A bad debt or a bad debt recovery can be added using the New Bad Debt or the New Bad Debt Recovery button on the Financial → Payments page in the student's profile. Bad debts & bad debt recoveries are recorded in AR Card as separate transactions and change the student's balance.
Note: A new bad debt recovery can be added only if a bad debt exists:

Fill in the required fields and click the Add button:

All bad debts can be viewed on the Bad Debts and Bad Debt Recoveries panel. To change or delete the existing record, click on the amount value:

Then use Edit or the Delete buttons correspondingly:

All changes will be reflected in the student's AR Card:

Apart from the transactions, the AR Card has the Bad Debt field showing the debt amount that must be paid off. This amount is a sum of all bad debts minus bad debt recoveries.
If there is a Bad Debt that has not been paid off, you will see a notification about this unpaid debt on the following pages: "Student’s Name": Lead Details, Student "Student’s Name": Enrolled Details, Student "Student’s Name": Financial Details:

If a student has a debt, the student cannot be enrolled (EA cannot be populated) without special permission:

After adding the bad debt recovery, there is an ability to immediately create the Payment for that amount:

Fill in all the required information about the Payment and click the Add button:

The payment will be added to Received Payments as any other payment:

GEGI also allows importing bad debts and bad debt recoveries. More information can be found in the following article: How to Use the "Financial → Import" Tab?