diff --git a/lib/mv/vereinfacht/client.ex b/lib/mv/vereinfacht/client.ex
index 6a81c46..999bd44 100644
--- a/lib/mv/vereinfacht/client.ex
+++ b/lib/mv/vereinfacht/client.ex
@@ -98,13 +98,12 @@ defmodule Mv.Vereinfacht.Client do
 
   @sync_timeout_ms 5_000
 
-  # Resolved at compile time so Mix is never called at runtime (Mix is not available in releases).
-  @env Mix.env()
-
   # In test, skip retries so sync fails fast when no API is running (avoids log spam and long waits).
+  # `sql_sandbox?/0` reads runtime config (true only in test) and avoids calling Mix at runtime,
+  # which is unavailable in releases.
   defp req_http_options do
     opts = [receive_timeout: @sync_timeout_ms]
-    if @env == :test, do: [retry: false] ++ opts, else: opts
+    if Mv.Config.sql_sandbox?(), do: [retry: false] ++ opts, else: opts
   end
 
   defp post_and_parse_contact(url, body, api_key) do