[error] No such file or directory: '../brom-payload/build/payload.bin'

[0xADB]

Hey,
by executing the fastboot-step.sh script and following the guide on https://forum.xda-developers.com/hd8-hd10/orig-development/fire-hd-8-2018-downgrade-unlock-root-t3894256 I had this error. Seems like payload.bin does not exist. Do I have to insert a payload.bin file? Am I doing something wrong or what is missing? I'm running the script as root user btw.

[full console output]

[2020-10-03 20:09:25.403094] Waiting for bootrom
[2020-10-03 20:09:29.667655] Found port = /dev/ttyACM0
[2020-10-03 20:09:29.668126] Handshake
[2020-10-03 20:09:29.668922] Disable watchdog

 * * * Remove the short and press Enter * * * 


[2020-10-03 20:09:35.608975] Init crypto engine
[2020-10-03 20:09:35.623829] Disable caches
[2020-10-03 20:09:35.624445] Disable bootrom range checks
Traceback (most recent call last):
  File "main.py", line 121, in <module>
    main()
  File "main.py", line 57, in main
    load_payload(dev, "../brom-payload/build/payload.bin")
  File "/home/[username]/amonet/modules/load_payload.py", line 96, in load_payload
    with open(path, "rb") as fin:
FileNotFoundError: [Errno 2] No such file or directory: '../brom-payload/build/payload.bin'

With kind greets from Germany :)