Title: Prototype app fails to load – Unable to fetch app definition / MONO_WASM error

AppSheet AppSheet Q&A
1

Hello AppSheet Community,

My prototype app cannot load in either Editor Preview or Direct Runtime.

Confirmed:

  • Editor loads successfully and reports “No issues found”

  • App definition, tables, columns, and Google Sheets source are accessible

  • Preview and Direct Runtime fail before data loading

  • The problem occurs on Chrome, Edge, notebook, and mobile

  • A known-good AppSheet sample loads in the same browser

  • No app configuration, schema, security setting, or data was changed during diagnosis

Errors:

  • Unable to fetch app definition. Error: A task was canceled.

  • Error initializing AppModel: Unable to fetch app definition.

  • MONO_WASM / WebAssembly.Module(): Invalid tag index

The app is currently Prototype / Not Deployed on a FREE account. Deployment Check reports that the app requires a paid plan because it uses sign-in and security filters.

However, AppSheet documentation states that prototype development and testing are available on the free plan.

Questions:

  1. Can the FREE-plan account status prevent the app owner from loading a prototype Runtime?

  2. Could this indicate an app-definition serialization or Runtime compilation issue?

  3. Is there any safe diagnostic step that does not require removing sign-in or security filters?

The full App ID and UTC timestamps can be provided privately if required.

2

This is an internal problem and can only be addressed by going through Support.

Attn @Jose_Arteaga

3

That is correct @Steve !

Hello @Kiattisak_Seedasome and Welcome to the AppSheet Community!

I will be sending you a PM shortly to follow up on this.

4

Hello @Kiattisak_Seedasome,

I sent you a PM as I need your help so that engineering team can further analyze your application. Please advise.

5

Closing the loop on this…

I have not received any response so far so I must close this thread.