I believe envoy.lua is a HTTP filter so filterType needs to be HTTP. This has worked for me.
In the 1.2 docs Istioldie 1.2 / Envoy Filter
Note 3 mentions that listenerProtocol must also be HTTP, theres also an example
There is also a new way of doing these EnvoyFilters but I had issues with it and had to use this deprecated format.
(although looks like there may be a workaround for my issue now.)