How to loop within an array to pull on ids

I am struggling in try to display all marketids from a json. At the moment I have a foreach to return each event id and all its related data from within markets array like so:

export async function generateData() {
  const matchArray = [];
  try {
    const data = await get(dataEndpoint);
    data ? data.forEach((item) => {
      if (item.type== 'MATCH'){
      matchArray.push({ eventId: item.id, markets: [item.markets]});
      } 
    }) : console.log(`No data received ${data}`);
    await writeJSON(matchFilePath, matchArray);
  } catch (error) {
    throw error;
  }        
}

It writes the following in the json file:

[
  {
    "eventId": "b312bea8-c25b-43f2-85a3-1c6caa5230e4",
    "markets": [
      [
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d26",
          "createdAt": "2024-08-05T10:31:58.288Z"
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d25",
          "createdAt": "2024-08-05T10:31:58.288Z"
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d21",
          "createdAt": "2024-08-05T10:31:58.288Z"
        }
      ]
    ]
  },
  {
    "eventId": "b312bea8-c25b-43f2-85a3-1c6caa5230e4",
    "markets": [
      [
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d16",
          "createdAt": "2024-08-05T10:31:58.288Z"
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d15",
          "createdAt": "2024-08-05T10:31:58.288Z"
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597121",
          "createdAt": "2024-08-05T10:31:58.288Z"
        }
      ]
    ]
  }
]

But ideally what I want is only all the ids within markets[] for each event, so based on the above json example I want it to be displayed like this:

[
  {
    "eventId": "b312bea8-c25b-43f2-85a3-1c6caa5230e4",
    "markets": [
      [
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d26",
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d25",
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d21",
        }
      ]
    ]
  },
  {
    "eventId": "b312bea8-c25b-43f2-85a3-1c6caa5230e4",
    "markets": [
      [
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d16",
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597d15",
        },
        {
          "id": "28e53502-8a44-467e-a5bc-d1d613597121",
        }
      ]
    ]
  }
]

I’m not sure how pull only the market ids within the markets[] array. Curious to know how to do this.