Problem with 2.90in-b waveshare display

Hello,

I trying to get my display with the 3-color Waveshare display running on my ESP32DEVKITV1
Using the supplied demo code from Waveshare shows me, that the screen is running fine.

But the following code is not working.
Yes, I know, esphome does not support the red colour at the moment, but B/W should work.
The screen is black and goes to white and back to black periodically

font:
  - file: 'fonts/Antenna Bold.ttf'
    id: font1
    size: 12
    
spi:
  clk_pin: GPIO13
  mosi_pin: GPIO14

display:
  - platform: waveshare_epaper
    cs_pin: GPIO15
    dc_pin: GPIO27
    busy_pin: GPIO25
    reset_pin: GPIO26
    model: 2.90in-b
    update_interval: 60s
    reset_duration: 2ms
    id: my_display
    pages:
      - id: page1
        lambda: |- 
           ESP_LOGI("display", "Updating display");
           it.rectangle(20, 50, 30, 30);
           ESP_LOGI("display", "After drawing");

What is wrong/missing?
Thank you in advance!