how to query for all item in a partition, getting all sort keys

[Bryson14]

I have a table where "user_id" is the partition key and "conversation_id" is the sort key. In this case, I want to get all conversations belonging to a particular user. So my query looks like this:

let response = client
        .query()
        .table_name(&table_name)
        .key_condition_expression("#hk = :hv")
        .expression_attribute_names("#hk", TableName::Conversation.get_partition_key())
        .expression_attribute_values(":hv", AttributeValue::S(user_id.clone()))
        .send()
        .await;

TableName::Conversation.get_partition_key() return user_id

This is that whenever I run this, it returns a SDK error called service error

I've made sure dynamo db matches this schema too

Any help?