How do I update Redux store with POST response?

I have an application that is using React, Redux (Redux Thunk). I having an issue updating the state in the reducer after a fetch post inserts into a table. I am trying to dispatch an action and pass some information from the action to the reducer but not able to do so. I am specifically trying to pass the fetch response into the dispatch. I have a key named res within my dispatch. I set it to a value of data but I believe this value of data is undefined.

export function insertSearchTerm(searchTerm) {
  console.log('C')
   return (dispatch) => {
     fetch('http://localhost:3001/api/v1/searches?searchterm='+ searchTerm, {
        headers: {
          'Content-Type':'application/json',  //headers - tells y9ou that it is json
        },
        method:'POST',
        body: JSON.stringify(searchTerm)          //stringifies searchTerm
      }).then(res => console.log('Inside insertSearch Term resp', res.json()))
        .then(data => {
            dispatch({
               type:'INSERT_SEARCH_TERM',
               searchTerm: searchTerm,
               res : data
            })
          }
        )
      }
     console.log('E')
   }

export default function allSearchTermsReducer(state = {allSearchTerms: []}, action) {
  switch (action.type) {
    case 'ALL_SEARCHES':
      console.log("Allsearch reducer",action.payload);
      return {...state, allSearchTerms: action.payload}
    case 'INSERT_SEARCH_TERM':
      console.log('insert search term action', action)
      return {
          ...state,
          allSearchTerms: [...state.allSearchTerms, action.id, action.searchTerm, action.created_at] }
    default:
      return state
  }
};