Custom Node Builder showing "Application error: client-side exception" - cannot access saved node

[Jonathon]

I successfully created and tested a custom QuickBooks integration node called “QuickBooks Online Vendor Bills Creator” but now cannot access the custom node builder due to a client-side exception error.

Issue:

• Custom node was working perfectly in tests
• When trying to finalize/save the node, getting “Application error: a client-side exception has occurred”
• Error persists in incognito mode and different browsers
• Main Gumloop platform works fine - only custom node builder affected

Browser Console Errors:

• CORS policy blocking API calls to api.gumloop.com
• “Cannot read properties of undefined (reading ‘toLowerCase’)” errors
• Multiple JavaScript framework failures

Environment:

• Main Browser: Chrome
• Operating System: MacOS

Request:

1. Can you confirm if my “QuickBooks Online Vendor Bills Creator” node is saved in my workspace?
2. How can we resolve this issue?

[Gumloop_Bot]

Hey @Jonathon! If you’re reporting an issue with a flow or an error in a run, please include the run link and make sure it’s shareable so we can take a look.

1. Find your run link on the history page. Format: https://www.gumloop.com/pipeline?run_id={{your_run_id}}&workbook_id={{workbook_id}}

2. Make it shareable by clicking “Share” → ‘Anyone with the link can view’ in the top-left corner of the flow screen.
   

3. Provide details about the issue—more context helps us troubleshoot faster.

You can find your run history here: https://www.gumloop.com/history

[Jonathon]

Detailed Technical Errors (for Engineering Team):

1. CORS Preflight Failure:

   • OPTIONS request to https://api.gumloop.com/ returning non-200 status
   • Browser blocking subsequent fetch requests
   • Error: “Response to preflight request doesn’t pass access control check”

2. Chrome Extension Messaging Error:

   • “A listener indicated an asynchronous response by returning true, but the message channel closed before a response was received”
   • Suggests extension listener not properly calling sendResponse()

3. JavaScript Runtime Errors:

   • TypeError: Cannot read properties of undefined (reading ‘toLowerCase’)
   • Multiple framework initialization failures

Node Details:

• Node Name: “QuickBooks Online Vendor Bills Creator”
• Functionality: Creates vendor bills in QBO using Company ID parameter
• Status: Built and tested successfully before save attempt
• Integration: QuickBooks Online OAuth2 API

[Wasay-Gumloop]

Hey @Jonathon – I can see that the node is saved on your profile, do you mind opening a new workflow, and searching for “QuickBooks Online Vendor Bills Creator” in the node library and adding it to the workflow? Does that work or does it still throw an error?

[Jonathon]

It still throws the error

[Wasay-Gumloop]

That is odd. Thank you for trying. Would it at all be possible to screen record that as well? I’m very sorry for the hassle. I’m trying to reproduce this on my end, and I’m not exactly sure under what circumstances this happens. Does this happen as soon as the node is added to the canvas? Are you able to share the node? I’m assuming that you’re not able to access the node at all. But regardless, the node is safe. I’m just trying to investigate here so we can push a fix for this.

[cvgrubbs]

Having the same problem with custom nodes. 2 different new nodes, same result. Older built custom nodes still work.

[Wasay-Gumloop]

Hey @Jonathon – This issue should be fixed now. That said, you’d have to create a new custom node from scratch unfortunately. Really sorry for the trouble here!

@cvgrubbs Your custom nodes should work as is, there was a slightly different issue here.

[Jonathon]

@Wasay-Gumloop Thanks a lot, I was able to recreate it and successfully test run the custom node.

[cvgrubbs]

Working now. Thanks.

Is there any way to use the old custom builder? The new one is awful.

[Wasay-Gumloop]

Yes we’ll explore a Manual Build option.

[cvgrubbs]

Any timeline for this? It’s so bad now. I’ve spent hours trying to get gummie to function. Gemini will correct the code, it functions fine, gummie overwrites it and breaks again.

[Wasay-Gumloop]

Should be soon. You could use the Run Code instead if you prefer writing the code yourself.