📝 Add custom domain troobleshoot section

apps/docs/docs/editor/custom-domain.md

@@ -17,3 +17,15 @@ To connect a new domain, follow the instructions:
 />
 
 Once you've added the corresponding DNS record, click on the "Save" button. You might have to wait for a few minutes before the record is properly propagated.
+
+## Troobleshooting
+
+If your domain is not properly configured or verified, you will see this error icon next to your domain link:
+
+<img
+  src="/img/custom-domain/invalid-config.png"
+  width="500"
+  alt="Error icon"
+/>
+
+Make sure to click on it to see what is required to do to fix the issue.