[Bug]: Azure image generation fails with `invalid_header` due to trailing semicolon in `Content-Type`

[VerunicaM]

What happened?

When using litellm.image_generation with unknown (newly added) Azure models (e.g., azure/FLUX-1.1-pro), the API call fails with:

15:29:31 - LiteLLM Proxy:ERROR: endpoints.py:158 - litellm.proxy.proxy_server.image_generation(): Exception occured - litellm.BadRequestError: AzureException - {"error":{"code":"invalid_header","message":"Header 'Content-Type' has invalid value `application/json;`","details":"Header 'Content-Type' has invalid value `application/json;`"}}. Received Model Group=FLUX-1.1-pro        
Available Model Group Fallbacks=None LiteLLM Retried: 1 times, LiteLLM Max Retries: 2
INFO:     127.0.0.1:57389 - "POST /images/generations HTTP/1.1" 400 Bad Request

This is caused by the Content-Type request header being set to application/json; (with a trailing semicolon), which Azure rejects as an invalid value.

---

Steps to Reproduce

import litellm

def main():
    litellm.api_base = "<my-azure-endpoint>"
    litellm.api_key = "<my-azure-api-key>"
    litellm.api_version = "2025-04-01-preview"

    litellm._turn_on_debug()

    result = litellm.image_generation(
        model="azure/FLUX-1.1-pro",
        prompt="A photograph of a red fox in an autumn forest",
        size="1024x1024"
    )

    print(result["data"][0]["url"])

if __name__ == "__main__":
    main()

---

Actual Behavior

• The request fails with a 400 Bad Request and invalid_header error from Azure.

---

Expected Behavior

• The Content-Type header should be exactly:

Content-Type: application/json

(no trailing semicolon), allowing the Azure API to accept the request and return the generated image URL.

Relevant log output

15:29:31 - LiteLLM Proxy:ERROR: endpoints.py:158 - litellm.proxy.proxy_server.image_generation(): Exception occured - litellm.BadRequestError: AzureException - {"error":{"code":"invalid_header","message":"Header 'Content-Type' has invalid value `application/json;`","details":"Header 'Content-Type' has invalid value `application/json;`"}}. Received Model Group=FLUX-1.1-pro        
Available Model Group Fallbacks=None LiteLLM Retried: 1 times, LiteLLM Max Retries: 2
INFO:     127.0.0.1:57389 - "POST /images/generations HTTP/1.1" 400 Bad Request

Are you a ML Ops Team?

No

What LiteLLM version are you on ?

v1.75.5

Twitter / LinkedIn details

No response

[ishaan-jaff]

resolved with PR