## The symptom
Calling `listTabs` via the `EnvelopesApi` in docusign/esign-client throws a
fatal "Class 'Number' not found" from `ObjectSerializer.php`. During
deserialization the SDK passes the bare class name `Number` to the deserializer
instead of the namespaced `DocuSign\eSign\Model\Number`, so PHP cannot
resolve it. Reported on a Laravel 5.x app using docusign/esign-client ^3.0, and
reproduced by several other users.
## The proper fix
Upgrade: the maintainer reports the bug (DCM-3210) is fixed in SDK v5.1.
```
composer require docusign/esign-client:^5.1
```
## Workaround if you cannot upgrade
Edit `vendor/docusign/esign-client/src/ObjectSerializer.php` and replace the
bare `Number` class reference with the fully qualified
`\DocuSign\eSign\Model\Number`. A community member confirmed this fixes the
fatal. Note that vendor edits get wiped on the next `composer install`, so treat
it as temporary.