Bug Report: HTTP Integration Custom Headers Not Being Sent

carlos_eduardo · February 10, 2026, 8:09pm

Issue Summary:

Custom headers configured in HTTP integration are not being transmitted in actual requests, causing Supabase UPSERT operations to fail.

Expected Behavior:

Header Prefer: resolution=merge-duplicates should be sent to enable UPSERT functionality (create if not exists, update if exists).

Actual Behavior:

Header is configured correctly in Plasmic Studio
Header does not appear in network requests (verified via DevTools)
Results in 409 Conflict errors instead of successful UPSERT

Technical Evidence:

Configuration: Header Prefer: resolution=merge-duplicates set in HTTP integration
Network Analysis: DevTools shows no “Prefer” header in request headers
Error: Consistent 409 Conflict with duplicate key constraint violation
Reproducible: Multiple tests confirm header transmission failure

Impact:

Prevents UPSERT operations, forcing workarounds that compromise intended functionality.

Environment:

Integration: HTTP (Supabase REST API)
Operation: POST
Expected Header: Prefer: resolution=merge-duplicates

This appears to be a known issue where HTTP integration custom headers are inconsistently transmitted.

alex_noel · February 11, 2026, 2:09pm

Hi! @carlos_eduardo
Are you referring to the deprecated integration (Data Query HTTP integration), or the one that we released yesterday (Fetch integration)?
I believe it should be fixed in the newest version

carlos_eduardo · February 11, 2026, 2:34pm

So you’re admitting there’s a real bug with Prefer: resolution=merge-duplicates in the Data Query HTTP integration I’m using? Am I supposed to just sit idly by while you fix it?

samuel_pullman · February 13, 2026, 9:21am

Hi @carlos_eduardo, unfortunately we are deprecating the old database integrations. As Alex mentioned, we have soft released a new fetch integration that doesn’t have this bug.