Using gemini-2.5-flash-image-preview - advice and help needed

[lastrider04]

I've added gemini/gemini-2.5-flash-image-preview as a new model using the UI add model, however when I test it works fine with /chat/completions but not with images/generation.

litellm.APIConnectionError: GEMINI_API_KEY is not set
Traceback (most recent call last):
  File "/usr/lib/python3.13/site-packages/litellm/images/main.py", line 452, in image_generation
    return llm_http_handler.image_generation_handler(
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        model=model,
        ^^^^^^^^^^^^
    ...<7 lines>...
        client=client,
        ^^^^^^^^^^^^^^
    )
    ^
  File "/usr/lib/python3.13/site-packages/litellm/llms/custom_httpx/llm_http_handler.py", line 2713, in image_generation_handler
    headers = image_generation_provider_config.validate_environment(
        api_key=litellm_params.get("api_key", None),
    ...<4 lines>...
        litellm_params=dict(litellm_params),
    )
  File "/usr/lib/python3.13/site-packages/litellm/llms/gemini/image_generation/transformation.py", line 116, in validate_environment
    raise ValueError("GEMINI_API_KEY is not set")
ValueError: GEMINI_API_KEY is not set

stack trace: Traceback (most recent call last):
  File "/usr/lib/python3.13/site-packages/litellm/images/main.py", line 452, in image_generation
    return llm_http_handler.image_generation_handler(
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        model=model,
        ^^^^^^^^^^^^
    ...<7 lines>...
        client=client,
        ^^^^^^^^^^^^^^
    )
    ^
  File "/usr/lib/python3.13/site-packages/litellm/llms/custom_httpx/llm_http_handler.py", line 2713, in image_generation_handler
    headers = image_generation_provider_config.validate_environment(
        api_key=litellm_params.get("api_key", None),
    ...<4 lines>...
        litellm_params=dict(litellm_params),
    )
  File "/usr/lib/python3.13/site-packages/litellm/llms/gemini/image_generation/transformation.py", line 116, in validate_environment
    raise ValueError("GEMINI_API_KEY is not set")
ValueError: GEMINI_API_KEY is not set

During handling of the above exception, another exception occurred:

Traceback (most recent call 

I've also tried adding {"mode": "image_generation"} in model info

Any ideas why this could be?

I am using openweb UI so the idea is to do the image generation there via LiteLLM.

Help appreciated!