You can download the sources from Github.
For the webclient : https://github.com/Quopt/ITR-webclient
For the Python REST API : https://github.com/Quopt/ITR-API
All source code is licensed by Quopt IT Services BV to you or your organisation under a modified version of the Artistic 2.0 open source license.
The webclient repository contains open source components from other suppliers. Please review their license agreements as well. The REST API uses other open source libraries which may have their own licensing agreements as well.