Working on the same thing right now, as far as I understand you can call the script via the webhook directly “…/script/your_script?api…” so there is no need for the “entity_id” in the body. For passing a value, put
{"value1" : "{{TextField}}" }
in your body and then use “value1” simply as your varaible in your script. As far as I know that should work.
Glad you could solved it.
Got mine up and running just a sec ago too. https://xxx.duckdns.org/api/services/script/some_script?api_password=password
at least worked for me (without the need of passing the entity_id then), don’t know why it wouldn’t work for you though.