Uploaded assets are disappearing/expiring after a few days

We are using the PDF Services document generation API (https://developer.adobe.com/document-services/docs/overview/pdf-services-api/howtos/api-usage/) for generating documents. When we upload a template using the POST https://pdf-services.adobe.io/assets API call, the asset works fine for document generation for a few days. However, after a few days, the API call to generate a document starts producing the following error:

{
    "error": {
        "code": "NOT_FOUND",
        "message": "Asset Not Found."
    }
}

At that point, we have to upload a new template and update the asset ID used to generate the document. How can we make it so the template asset does not expire and we can continue to generate documents from the same template?