Do you have ThinOS 9.1.5067 Microsoft AVD package v1.5_1325 for Dell Wyse 3040, 5070, 5470, and 5470 All-in-One Thin Clients installed?
https://dl.dell.com/FOLDER08003895M/1/Microsoft_AVD_1.5_1325.zip
Download and extract. Then upload into WMS as a package for 9.1. Then go to your policy and under the Firmware section, select application, and select the AVD package to install on your device.