The Order APIs allow users to create and manage checkout sessions for both eBay members and eBay guest users. Using the methods in these APIs, users can create and update a checkout session, apply coupons and add-ons to the session, pay for an order, and retrieve information on said orders. 

There are two different versions of the Order API:

• The Order API v1 can be used to create and manage eBay member checkout sessions. A member checkout involves a buyer that is logged into their eBay account and can use information stored with their account, such as their payment and shipping details, to purchase an item. Applications integrating with this checkout method must comply with Payment Card Industry Data Security Standards (PCI DSS) to ensure proper handling of sensitive credit card data.
• The Order API v2 can be used to create and manage eBay guest checkout sessions. A guest checkout involves a buyer that does not have or  is not logged into an eBay account. Their information must be collected in order to purchase and ship an item, and the order is completed through the Checkout with eBay widget. For more details about the Checkout with eBay widget, see Integrating the Checkout with eBay button.

The Order API v1 methods used to create and manage an eBay member checkout session are discussed below: 

1. Create a member checkout session and add items to your cart using InitiateCheckoutSession. The key containers required for the request are briefly described below: 
   • lineItemInputs: An array of the line items being added to the cart during the checkout session. 
   • creditCard (optional): The buyer’s credit card information. This container is not required unless the member is using a credit card different from the one on file. 
   • shippingAddress (optional): The shipping address information for the order associated with the checkout session. This container is not required unless the member is using a shipping address different from the one on file. 

   If the call is successful, information about the checkout session will be returned in the response. The following key containers and fields will be returned in the response: 

   • acceptedPaymentMethods: An array of accepted payment methods that can be used to purchase the order. 
   • checkoutSessionId: The unique eBay identifier of the checkout session.

     Note: This value is used as a URI parameter for the other checkout methods. Users should keep track of this value as there is no programmatic way to retrieve it at this time.

   • ExpirationDate: The time and date, in UTC format, when the checkout session will expire. 
   • shippingOptions: An array of shipping options that are available for the order. By default , the first returned shipping option will be selected. See the next step for instructions on how to change the shipping option for an order. 
   • pricingSummary: The total cost of all the line items in the order. 
2. If needed, change the shipping method for a specified line item in the order using updateShippingOption. This method can be used if the buyer does not want to use the first returned shipping option automatically selected when creating a checkout session. See the shippingOptions container in the InitiateCheckoutSession response to see all available shipping options for a line item, including their cost and expected delivery date range.
3. Place and pay for the order using placeOrder. The purchaseOrderId for the order will also be returned, which will be needed to retrieve details on the order in the next step. 
4. Review and retrieve details of the purchase order using getPurchaseOrder. This method can also be used to check if an order payment has cleared by checking the value of the purchaseOrderPaymentStatus field, and the fulfillment status of the item by checking the lineItemStatus enum.

The Offer API allows users to bid on a specific auction item on behalf of a buyer, setting a maximum amount they are willing to spend on the item. eBay will then make offers up to this amount, notifying the user if they have been outbid or if the bid has exceeded this set amount. Users can also retrieve the bidding details specific to the buyer of a specific auction using this API. 

The API methods used to bid on an auction item are discussed below: 

1. Optionally, use the Browse API search method to find an auction item the buyer wants to bid on. For example, the following filter can be used to search only for auction items: filter=buyingOptions:{AUCTION}. Buyers can also check the returned currentBidPrice container to see the current highest bid price for an auction item. For more information on retrieving items using the Browse API, see the Inventory Discovery and Refresh Guide.
2. Use placeProxyBid to place a proxy bid for a specific auction item on behalf of a buyer, up to a maximum amount set by the buyer. You must pass in the item_id of the item you are bidding for, as well as the maximum amount (maxAmount) the buyer is willing to bid for the item. Multiple bids may occur up to the maxAmount value, with each bid being erased by a higher bid from another user. This value should be higher than the currentBidPrice  retrieved in the previous step.
3. Use getBidding to retrieve the bidding details for a specific auction. If the auction is still ongoing, the current highest bid amount of the item will be returned in the currentPrice container. If this amount is higher than the buyer’s set maxAmount, call placeProxyBid again to increase this max bid amount. The buyer’s current proxy bid is also returned through the currentProxyBid container, and the suggestedBidAmounts container will return a suggested bid amount for the next bid. Once the auctionStatus is ENDED, the value of highBidder will be returned as true if the buyer has won the auction.