rtsp fails with ug_input

[Xoffio]

I am trying to send the data from uv sender to uv receiver. I want the uv receiver to start the rtsp server, but it seems to fail.
This is what I am doing:

# Sender
./uv -t testcard2 -c libavcodec:codec=VP9:subs=420 -P 6004 TARGET_ip

# Receiver
./uv -t ug_input:6004:codec=VP9 -x rtsp

I get an output like this:

[lavc] Setting codec parameter crf to 22.000000
[lavc] Setting CRF to 22.00.
[lavc] Setting codec parameter preset to veryfast
[lavc] Setting codec parameter tune to zerolatency,fastdecode
[lavc] Setting thread count to 0, type: (other)
[lavc libx264 @ 000001d3fc42ad00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[lavc libx264 @ 000001d3fc42ad00] profile High, level 4.0, 4:2:0, 8-bit
[lavc] Selected pixfmt: yuv420p
[lavc] Failed to find a way to convert VP9 to yuv420p
[lavc] Attempting to use swscale to convert from vaapi to yuv420p.
Could not allocate raw picture buffer
[lavc] Failed to get sws input conversion.
[lavc] Using codec: H.264, encoder: libx264
[lavc] No direct decoder format for: VP9. Trying to convert with swscale instead.

Is there any way to do something like this?