dynamodb.transactWriteItems is not a function error on Lambda but not when using VS Code

I have successfully tested dynamodb.transactWriteItems using VS Code (node js) but when I moved my code to Lambda, it always throws the Type Error: dynamodb.transactWriteItems is not a function. Note that I am NOT using documentClient so declaring dynamodb = new AWS.DynamoDB() is not the solution.

How can I check the AWS-SDK used by Lambda (my npm aws-sdk is v2.372.0) and how do I make use of the proper AWS-SDK version on Lambda if this is the root cause of the issue?

data = await dynamodb.transactWriteItems({
  ReturnConsumedCapacity: "INDEXES",
  ReturnItemCollectionMetrics: "SIZE",
  TransactItems: [
      {
          Put: {
            TableName: envVarPOTableName,
            Item: {
              "poNumber": {S: poNumber}, 
              "supplierName": {S: event.supplierName},
              "poStatus" : {S: "Created"},
              "rmItemsArr": {L: [
                { M:{
                  "type": {S:event.rmItemObj.type}, 
                  "description": {S:event.rmItemObj.description}
                  },
                }
              ]}
            }
          }
      },
      {
        Update: {
          TableName: envVarRMTableName,
          Key:{
            "type": {S: event.rmItemObj.type},
            "description": {S: event.rmItemObj.description}
          },
          UpdateExpression: "set #pnA = list_append(#pnA, :vals)",
          ExpressionAttributeNames: {
            "#pnA" : "poNumbersArr"

          },
          ExpressionAttributeValues:{
            ":vals" : {L:[{S:poNumber}]}

          },
          ReturnValuesOnConditionCheckFailure: "ALL_OLD"
        }
      }
]
}).promise();