I'm trying to retrieve a full list of Seller items for sale using GetSellerList on a sandbox account. I am using PHP on my website to do this.
I have successfully gone through the process of authentication and received an access token via the client_credentials method. I am now trying to to call GetSellerList using this token via the xml method as shown on this page: https://developer.ebay.com/devzone/xml/docs/reference/ebay/GetSellerList.html#Input
However, the api is returning the message "Invalid IAF token", along with "21916984ErrorRequestError1173E1173_CORE_APISELLING_19187371_R1"
It does not offer any advice as to why it is invalid, and I cannot find a troubleshooting section in the docs.
Does anyone know what would cause this? A specific scope required perhaps? Or is GetSellerList the best method to use? All I want to do is retrieve a list of items for sale to display them on my site.