Prompt template cannot access tool_schema

[KokoDoko]

I created a tutorial chatflow to learn how the tool agent works. I connected a prompt tempate to a tool and a LLM. Without the tool it works, but with the tool I get this error:

Missing value for input variable tool_schema

My tool has no input schema, it only outputs a random number. I tried adding an input schema but that didn't help.
My prompt template uses the schema like this : {tool_schema} .

I have no idea how to fix this error, all my settings seem to be correct. I hope someone here can explain how to integrate tool calling in the prompt template? See the screenshot for my flow: