[Python] GraphQL mutation via Ariadne in FastAPI returns 400 error despite correct schema —...

I’m building a FastAPI microservice that exposes a GraphQL endpoint using Ariadne. It implements a TextCleaner node in a modular workflow engine.

type Mutation {
cleanText(context: ExecutionContextInput, state: CleanTextInput): CleanTextOutput
}

input ExecutionContextInput {
executionId: String!
}

input CleanTextInput {
text: String!
}

type CleanTextOutput {
response: CleanTextResponse
}

type CleanTextResponse {
text: String
}



When I try to call the mutation from Python using httpx:

import httpx

query = """
mutation CleanText($context: ExecutionContextInput!, $state: CleanTextInput!) {
cleanText(context: $context, state: $state) {
response {
text
}
}
}
"""

variables = {
"context": { "executionId": "123" },
"state": { "text": "Hello World!!" }
}

resp = httpx.post(
"http://localhost:8000/graphql",
json={"query": query, "variables": variables}
)

print(resp.status_code)
print(resp.text)



I keep getting:

400 Bad Request
{"errors": [{"message": "Invalid GraphQL request"}]}


Verified schema with graphql-core introspection

Mutation works in GraphQL Playground

Using the same JSON body in curl works fine

httpx GET requests work for queries but not POST for this mutation

What’s the correct way to structure and send the GraphQL mutation from Python so Ariadne doesn’t return a 400 error?

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