Control account

Hi everyone! I am studying FA module of ACCA .I was doing some exam exercises and I have a doubt in this question because I do not fully understand why discounts allowed is included on the credit side of the receivables control account. Thank you so much. I appreciate your help. On 1 April 20X8 Brendon was owed $61,784 by his credit customers. During the year to 31 March 20X9 his credit sales totalled $660,846, discounts allowed totalled $11,945, irrecoverable debts were $6,150 and dishonoured cheques amounted to $250. The amount received from credit customers during the year was $655,135. On 31 March 20X9, Brendon was owed $52,278 from his credit customers. What was the amount of interest was charged to credit customers for late payment during the year ended 31 March 20X9? The answer is:2628