Next.js 15: Environment variables missing in API Routes

[gebhardtsascha-4135 (Sircrash)]

I’m experiencing a critical issue where ALL non-NEXT_PUBLIC_ environment variables are unavailable at runtime in Next.js API Routes (Route Handlers), even though they’re correctly configured in the Vercel dashboard. This is blocking production functionality that requires server-side environment variables like SUPABASE_SERVICE_ROLE_KEY.

Current versus Expected behavior:

Current Behavior:

• All non-NEXT_PUBLIC_ environment variables are completely missing from process.env at runtime in API Routes
• SUPABASE_SERVICE_ROLE_KEY is not available (returns undefined)
• TEST_SERVICE_KEY (test variable) is also not available
• Only NEXT_PUBLIC_* variables work correctly

Expected Behavior:

• All environment variables set in Vercel dashboard should be available in process.env at runtime in API Routes
• SUPABASE_SERVICE_ROLE_KEY should be accessible via process.env.SUPABASE_SERVICE_ROLE_KEY
• Both NEXT_PUBLIC_* and non-NEXT_PUBLIC_ variables should work

Test Endpoint Results:
I created a test endpoint (/api/test-env) that checks available environment variables:
{
“hasSupabaseServiceRoleKey”: false,
“hasTestServiceKey”: false,
“availableSupabaseVars”: [“NEXT_PUBLIC_SUPABASE_ANON_KEY”, “NEXT_PUBLIC_SUPABASE_URL”],
“allEnvVarNames”: [/* SUPABASE_SERVICE_ROLE_KEY and TEST_SERVICE_KEY are completely missing */]
}Code, configuration, and steps that reproduce this issue:

**Test Endpoint Code:**ipt
// app/api/test-env/route.ts
import { NextRequest, NextResponse } from “next/server”;

export async function GET(request: NextRequest) {
const envCheck = {
hasSupabaseServiceRoleKey: !!process.env.SUPABASE_SERVICE_ROLE_KEY,
hasTestServiceKey: !!process.env.TEST_SERVICE_KEY,
availableSupabaseVars: Object.keys(process.env)
.filter((key) => key.includes(“SUPABASE”) || key.includes(“TEST”))
.sort(),
};
return NextResponse.json(envCheck, { status: 200 });
}API Route Example (failing):
// app/api/search-players/route.ts
export async function GET(request: NextRequest) {
const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY; // Returns undefined
// … rest of code fails because key is missing
}next.config.ts:
import type { NextConfig } from “next”;

const nextConfig: NextConfig = {
output: process.env.CAPACITOR_BUILD === ‘true’ ? ‘export’ : undefined,
skipTrailingSlashRedirect: true,
// No env section - was removed as suggested by support
};

export default nextConfig;Steps to Reproduce:

1. Set SUPABASE_SERVICE_ROLE_KEY in Vercel dashboard (all environments enabled)
2. Deploy to Vercel
3. Call /api/test-env endpoint
4. Observe that hasSupabaseServiceRoleKey: false

Troubleshooting Steps Already Taken:

1. Verified variables are set in Vercel dashboard for all environments (Production, Preview, Development)
2. Multiple redeployments performed (with and without build cache)
3. Removed env section from next.config.ts (was suggested by support)
4. Downgraded from Next.js 16 RC to stable Next.js 15.5.6
5. Created test variable TEST_SERVICE_KEY to rule out name-specific issues
6. Verified Route Handlers are correctly implemented (app/api/*/route.ts)

Project information (URL, framework, environment, project settings):

• Project URL: https://neonarc.de
• Framework: Next.js 15.5.6 (App Router)
• React: 18.3.1
• Deployment: Vercel Production
• Environment: Production (VERCEL_ENV=production)
• Route Handlers: app/api/*/route.ts structure
• Variables Set in Dashboard:
  • NEXT_PUBLIC_SUPABASE_URL (works)
  • NEXT_PUBLIC_SUPABASE_ANON_KEY (works)
  • SUPABASE_SERVICE_ROLE_KEY (doesn’t work)
  • TEST_SERVICE_KEY (doesn’t work)

Impact:
This is blocking critical production functionality:

• Player search API routes
• Contact request management
• User blocking/unblocking
• Direct messaging

Question:
Has anyone else experienced this issue where ALL non-NEXT_PUBLIC_ environment variables are unavailable in Next.js Route Handlers on Vercel? Is there a project-specific setting or configuration that could be affecting this?

Any help or insights would be greatly appreciated!
Sascha