AWS CDK new LambdaFunction cannot find functionArn – Amazon web services

Whilst building a new LambdaFunction, with the AWS CDK aws-lib, I am encountering an issue when integrating the Lambda with the httpApi on API Gateway.

Expected result: Have a Lambda function trigger upon posting to a method on the httpApi resource.

Error message: "TypeError: Cannot read properties of undefined (reading ‘functionArn’)"

Lambda Function:

async function handler(event) {
  return {
    body: JSON.stringify({ message: "SUCCESS " }),
    statusCode: 200,
  };
}

module.exports = { handler };

Lambda Stack:

export class LambdaStack extends Stack {
  public readonly lambdaFunction: LambdaFunction;

  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);

    const resourceEnvironment: ResourceEnvironment = {
      account: Stack.of(this).account,
      region: Stack.of(this).region,
    };

    const lambdaFunction = new LambdaFunction(
      this,
      "lambdaFunction",
      {
        runtime: Runtime.NODEJS_16_X,
        memorySize: 1024,
        timeout: Duration.minutes(15),
        handler: "index.handler",
        code: Code.fromAsset(
          join(__dirname, "../services/lambdaFunction")
        ),
        environment: {
          REGION: Stack.of(this).region,
          AVAILABILITY_ZONES: JSON.stringify(Stack.of(this).availabilityZones),
          addCommandUserLambdaArn: "",
        },
      }
    );
  }
}

AWS API Gateway Integration:

interface ApiProps extends StackProps {
  lambdaStack: LambdaStack;
}

export class ApiStack extends Stack {
  declare restApi: Resource;

  constructor(scope: Construct, id: string, props: ApiProps) {
    super(scope, id, props);

    const { lambdaStack } = props;

    const lambdaFunctionIntegration = new HttpLambdaIntegration(
      "lambdaFunctionIntegration",
      lambdaStack.lambdaFunction
    );

    const httpApi = new HttpApi(this, "HttpApi", {
      apiName: "intoNS",
      corsPreflight: {
        allowHeaders: [
          "Content-Type",
          "X-Amz-Date",
          "Authorization",
          "X-Api-Key",
        ],
        allowMethods: [CorsHttpMethod.OPTIONS, CorsHttpMethod.POST],
        allowOrigins: ["*"],
        maxAge: Duration.days(10),
      },
    });

    httpApi.addRoutes({
      path: "/infoFIFO",
      methods: [HttpMethod.POST],
      integration: lambdaFunctionIntegration,
    });
  }
}