A return authorization number, or RA, is a unique number that companies issue to authorize you to return an item you have purchased if it is defective or just doesn't suit your needs. While not all retailers require a number, many do. Shipping a package without an RA number could cause problems.
Retailers use the RA number to track a return from the outset of the return to the end. Since large online retailers receive a number of packages for return, the RA number helps the retailer to know which credit belongs to which customer.
Either your shipping receipt or the company's website will provide directions on how to obtain an RA number. Usually, it can be generated online or acquired by calling the shipper.
The shipper will instruct you how to use the RA number. You might receive, via email, a label to print and affix to the package. That label will contain the RA. Otherwise, you will be instructed to write the RA on the package, on a return shipping label that came with your order or elsewhere.
When the item you send back is received by the shipper, its staff will verify the RA number and begin the crediting process. If you send an item without an RA number, the receiving staff might reject your package and send it back to you.
Once the shipper has received the merchandise and verified the product is the same one you purchased, the company will issue a credit. That could be credited to the credit card you used to pay for the item or via store credit, depending on the shipper's policy. The RA usually will have an expiration date; make sure to send the package so it is received before that date.