Hi @Jay ,
Thanks for reaching out. Could you please make sure all the Function activity settings are configured accordingly including the linked service?
Also I would recommend please try with body {"name":"@{activity('FilterFilesXML').output.Value}"} and see if that helps?
Here is a similar implementation (Azure Function activity) described by a community volunteer. Please have a look at it to see if that helps - Azure Data Factory - Copy the latest file with DATE PART to Folder using AZURE FUNCTIONS
Do let us know how it goes.
Thank you