You have been assigned to perform tests of controls on the sales system at ABC Company as part of the $31$ December $202$X audit. During testing, you noted the following errors:

$1.$ Invo m ice no$.54922$ issued on $12$ December $202$X was entered twice. The error was discovered when the customer rang to complain about being charged double the agreed amount.

$2.$ Invoice no$.59328$ issued on $18$ December $202$X matched the customer$$s order. However, the order was only partially filled because of a lack of stock in the warehouse, meaning items that were never delivered were included in the invoice. The error was discovered when the customer rang to complain about being overcharged.

$3.$ Invoice no$.62875$ issued on $29$ December $202$X was not processed through the usual channels. The details were correct but certain procedures, such as a formal credit check, were not documented. The invoice was a special order for a large project and amounted to around ten times the value of ABC$$s average invoices. The sale was personally handled by one of the directors and the invoice was prepared by his assistant.

Required: Treating each of the listed errors independently:

a$.$ Identify the assertions that are violated as a result of the errors listed above

b$.$ Describe the internal control weaknesses in the revenues process of ABC Company

c$.$ Describe the audit procedures that would be applied in relation to each of the errors