Resolve ReferenceError: "Application" is not defined. (Models.js#20) in Reference My Account

1. Navigate to Setup > Site Builder > SSP Applications.
2. Click on Edit for your deployed My Account SSP Application (e.g. Reference My Account, Custom My Account).
3. Check that the "commons.js" is added before "Models. js".
4. If not, swap their positions. These are the paths for commons.js and Models. js
Web Site Hosting Files/Live Hosting Files/SSP Applications/NetSuite Inc. - My Account/Reference My Account/ssp_libraries/commons.js

Web Site Hosting Files/Live Hosting Files/SSP Applications/NetSuite Inc. - My Account/Reference My Account/ssp_libraries/Models.js

5. Save.

As documented in SuiteAnswers topic SuiteCommerce Reference Implementation Web Assets, the order by which these files are listed on the SPP application record is important as they build on each other.