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Use the ReviseFixedPriceItem call to change the properties of a currently active fixed-price listing.
Here is a C# ReviseFixedPriceItem sample for revising a multi-variation item (adding and deleting a variation). This sample has been written using the .NET SDK v817.
*Prerequisite - make sure to have added an item with the SKU and variations below
Below is the code. Corresponding SOAP request is attached with this article.