validation error for StuffDocumentsChain document_variable_name context was not found in llm_chain input_variables: ['input'] (type=value_error)

Question

I'm trying to create a routing chain in langchain with different rags based on the route, each having a different prompt template, and this is the code I have:

period_template = """AAAText
Domanda:
{input}"""


ref_template = """BBBtext.
Domanda:
{input}"""

list_template = """CCCText.
Domanda:
{input}"""

prompt_infos = [
    {
        "name": "period",
        "description": "AAA",
        "prompt_template": period_template
    },
    {
        "name": "ref",
        "description": "BBB",
        "prompt_template": ref_template
    },
    {
        "name": "history",
        "description": "CCC",
        "prompt_template": list_template
    }
]

destination_chains = {}
for p_info in prompt_infos:
    PROMPT = PromptTemplate(template=p_info["prompt_template"], input_variables=["input"])
    chain = RetrievalQA.from_chain_type(
        chat_model,
        retriever=db.as_retriever(),
        return_source_documents=True,
        chain_type_kwargs={"prompt": PROMPT}
    )
    destination_chains[p_info["name"]] = chain

I get the error:

ValidationError: 1 validation error for StuffDocumentsChain root document_variable_name context was not found in llm_chain input_variables: ['input'] (type=value_error)

What's wrong and how can I resolve it?