# Backwards compatibilty

|             | T1C-GCL v1.x                                                                | T1C-GCL v2.x                                                           |
| ----------- | --------------------------------------------------------------------------- | ---------------------------------------------------------------------- |
| T1C-JS v1.x | OK                                                                          | OK, will use v1 fallback endpoint, only v1.2.5 functionality available |
| T1C-JS v2.x | NOK, will return error during initialisation until T1C-GCL upgraded to v2.x | OK                                                                     |

Initialising JS v2.x with an installed GCL v1.x will result in the following error:

```
new T1CLibException(400, '301',    'Installed GCL version is not v2 compatible. Please update to a compatible version.', client)
```

* HTTP status code: 400 Bad Request
* Error code: 301
* Error message: 'Installed GCL version is not v2 compatible. Please update to a compatible version.'

Attached to the error is a minimal client, which can be used to download a compatible GCL version.
