# Rendering errors

Lob occasionally encounters problems with the creative when rendering mailpieces; this can occur with either PDFs or HTML. To avoid sending out erroneous mailpieces, Lob provides visibility of these errors, with proactive notification of rendering errors in place. 

{% hint style="success" %}
We always recommend testing; and where possible, sending yourself a printed mailpiece. 
{% endhint %}

## PDF

**Lob will fail incorrectly formatted PDFs.** [See our PDF preflight checklist here](/print-and-mail/designing-mail-creatives/creative-formatting/pdf-preflight-checklist.md) to ensure your file will process through our rendering engine.

## HTML

**Lob will fail HTML that includes inaccessible assets (images, fonts, any other URLs):**

* the link to an asset is incorrect
* the asset referenced in the file is missing
* Lob has not been given the correct permission to access the asset (ensure that the link is set to public viewing, and not private)
* when a remote asset references a local asset (for example, a remote asset is at [www.example.com](http://www.example.com) which then references something local in that directory)
* slow or under-resourced server providing the asset (we recommend using a performant service, such as Amazon S3, to host the content)

### HTML Template Preview

If your HTML contains an inaccessible asset, your HTML preview will error. Details of the error will be displayed in a future release.

<figure><img src="/files/mVCUpYkpeuSlqtO5tMfw" alt="" width="375"><figcaption></figcaption></figure>

### In the Campaigns UI flow

* **When creating your Campaign, you&#x20;*****may*****&#x20;be notified when you generate a Creative Proof** (if the sample mailpiece that is rendered results in an error); if this occurs you should troubleshoot against the above list.

<figure><img src="/files/sAaKgcbvhao7koIsK4sZ" alt=""><figcaption></figcaption></figure>

* **After placing the order, you will be notified in the dashboard,** and the reason for the error will be provided (click to enlarge):

<figure><img src="/files/uYCekgFiKVVxipsWDTcY" alt=""><figcaption><p>Campaigns - dashboard</p></figcaption></figure>

<figure><img src="/files/he0AisFg4jvPqYeEE7tw" alt=""><figcaption><p>Campaigns - Form factor (ex: Postcards)</p></figcaption></figure>

<figure><img src="/files/S1KXtP5H2NS2OE5vX6eR" alt=""><figcaption><p>Campaigns - Form factor (ex: Postcards)</p></figcaption></figure>

<figure><img src="/files/HBjoFtkzDcgMz31sxQEN" alt=""><figcaption><p>Campaigns - order details</p></figcaption></figure>

* The Lob support team will proactively reach out.

### API users

* API customers will receive an error notification in the API response.
* The Lob support team will proactively reach out.

## Webhooks&#x20;

Webhooks users can subscribe to receive notifications of failed orders. (Learn more about [using webhooks](/print-and-mail/getting-data-and-results/using-webhooks.md) here.)

1. Under Webhooks in the dashboard, in the Live environment, click Create.
2. Check \[formfactor].failed; click Create.

<figure><img src="/files/G6VMFTMJ8wLE10FbxWgY" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/6ZZYoEsDDdpyLtp4gTZp" alt=""><figcaption><p>self_mailer.failed also available</p></figcaption></figure>

If subscribed to postcard.failed, letter.failed, and/or check.failed, and Lob fails an order during rendering, the following error messages are possible:

*"Rendering failed due to asset issue:*

* *The requested asset was not found: \<asset link>"*
* *The requested asset is not permitted: \<asset link>"*
* *Authentication is required to access the requested asset: \<asset link>"*
* *An internal server error occurred for: \<asset link>"*
* *The requested asset timed out: \<asset link>"*
* *An unknown server error occurred for: \<asset link>"*
* *The requested service is unavailable for: \<asset link>"*
* *An unknown error occurred for: \<asset link>"*

If not one of the most common errors above, or a PDF failure, *"try re-render”* will be returned.

<figure><img src="/files/6fOWcTjmr58jZJMRustT" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
If you are unable to resolve the error, please reach out to [support@lob.com](email:support@lob.com)
{% endhint %}


---

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