> ## Documentation Index
> Fetch the complete documentation index at: https://www.courier.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Throw on Variable Not Found
> Prevent messages from sending when required variables are missing. Checks only rendered blocks and shows errors in previews, logs, and observability integrations.
**Throw on Variable Not Found** prevents a channel from sending when a variable in rendered content cannot be resolved. Enable it in the notification template's **Settings > Advanced** section.
For example, if your email template includes `Hello {profile.first_name},` but `first_name` is missing from the user profile or the Send API `profile` object, Courier throws a render error for that channel. You can see the error in template preview and message logs:
**Preview**
**Logs**
## Conditional Blocks
The check runs after all conditionals are evaluated and only inspects blocks that will actually be sent. If a block is hidden by a condition, its variables aren't checked.
For example:
1. You add a conditional on `profile.first_name` to a text block.
2. The block uses `{profile.first_name}`.
3. The profile has no `first_name`, so the block is hidden by the condition.
4. Throw on Variable Not Found does not trigger, and the message sends successfully.
## Multiple Channels
Each channel is checked independently. If `{profile.first_name}` appears in your email template but not in your Inbox template, only the email channel fails; Inbox still renders and sends.
## Observability
Render errors from this feature appear in [Outbound Webhooks](/platform/workspaces/outbound-webhooks) and [Observability integrations](/external-integrations/observability/intro-to-observability) under channel update events.
## Related
Insert dynamic values from data, profile, tenant, and brand objects.
Control when notifications and channels send using conditional logic.