FastAPI: List of lists output throwing errors

Question

I have Python code that outputs list of lists. However, it will throw errors as many elements there are in the list. I tried both of these:

@app.post("/path/to/function", response_model = List[output])
# and
@app.post("/path/to/function", response_model = List[List[output]])

Error message:

pydantic.error_wrappers.ValidationError: 33 validation errors for HolidaysOut
response -> 0
  value is not a valid dict (type=type_error.dict)
response -> 1
  value is not a valid dict (type=type_error.dict)
...
response -> 32
  value is not a valid dict (type=type_error.dict)

I'm unsure where type_error.dict came from, because there are absolutely no dictionary objects. Or is this implying that I need to convert this into a list of dictionaries?