upload Url
URL to upload document image to.
Note that the upload URLs expire after 7 days. If an upload URL expires, you can refresh the URLs by retrieving the document upload from GET /account_holders/{account_holder_token}/documents.
Sets Builder.uploadUrl to an arbitrary JSON value.
You should usually call Builder.uploadUrl with a well-typed String value instead. This method is primarily for setting the field to an undocumented or not yet supported value.