firebase-admin experiencing Runtime.ImportModuleError on Lambda (Node v14)

Receiving this error when attempting to use the firebase-admin SDK on Node v14 on Lambda.

2022-05-13T21:41:25.923Z	undefined	ERROR	Uncaught Exception 	
{
    "errorType": "Runtime.ImportModuleError",
    "errorMessage": "Error: Cannot find module 'app'\nRequire stack:\n- /var/runtime/UserFunction.js\n- /var/runtime/index.js",
    "stack": [
        "Runtime.ImportModuleError: Error: Cannot find module 'app'",
        "Require stack:",
        "- /var/runtime/UserFunction.js",
        "- /var/runtime/index.js",
        "    at _loadUserApp (/var/runtime/UserFunction.js:202:13)",
        "    at Object.module.exports.load (/var/runtime/UserFunction.js:242:17)",
        "    at Object.<anonymous> (/var/runtime/index.js:43:30)",
        "    at Module._compile (internal/modules/cjs/loader.js:1085:14)",
        "    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)",
        "    at Module.load (internal/modules/cjs/loader.js:950:32)",
        "    at Function.Module._load (internal/modules/cjs/loader.js:790:12)",
        "    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:75:12)",
        "    at internal/main/run_main_module.js:17:47"
    ]
}

Here's the code attempting to import and use lambda:

import firebase from 'firebase-admin';

export const useFirebaseOnServer = () => {
  if (firebase.apps.length === 0) {
    return firebase.initializeApp({
      credential: firebase.credential.cert(require('./serviceAccount.json')),
      databaseURL: 'https://maskotter-f06cb.firebaseio.com',
    });
  }
  return firebase.app();
};

And finally my template.yaml file:

AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31
Description: >
  maskotter-email-forwarder

# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
  Function:
    Timeout: 6
    Tracing: Active

Resources:
  ForwarderFunction:
    Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
    Properties:
      CodeUri: forwarder/
      Handler: app.lambdaHandler
      Runtime: nodejs14.x
      Architectures:
        - x86_64
    Metadata: # Manage esbuild properties
      BuildMethod: esbuild
      BuildProperties:
        Minify: true
        Target: "es2020"
        Sourcemap: true
        EntryPoints:
          - app.ts

Been endlessly searching for an answer. Any help would be appreciated!