In case of goods sent on sale on approval basis, invoice has to be issued:

while sending the goods; another Invoice has to be issued by the recipient while rejecting the goods;
while sending the goods but the recipient can take credit only when the goods are accepted by him;
when the recipient accepts the goods or six months from the date of supply whichever isearlier.
when the recipient accepts the goods or three months from the date of supply whichever is earlier.

The correct answer is: C. when the recipient accepts the goods or six months from the date of supply whichever is earlier.

A sale on approval is a type of sale where the buyer is allowed to try the goods before they are obligated to purchase them. The seller typically sends the goods to the buyer on consignment, which means that the buyer does not own the goods until they are accepted. If the buyer does not accept the goods, they can be returned to the seller at no cost.

In the case of a sale on approval, the invoice must be issued when the recipient accepts the goods or six months from the date of supply, whichever is earlier. This is because the buyer does not own the goods until they are accepted, and the seller cannot bill the buyer for goods that they do not own.

Option A is incorrect because the invoice does not have to be issued while sending the goods. The invoice can be issued when the recipient accepts the goods or six months from the date of supply, whichever is earlier.

Option B is incorrect because the recipient can take credit for the goods when they are accepted, not when they are sent.

Option D is incorrect because the invoice does not have to be issued when the recipient accepts the goods or three months from the date of supply, whichever is earlier. The invoice can be issued when the recipient accepts the goods or six months from the date of supply, whichever is earlier.