Pro edition of Gantt; where to get source code

We are using the dhtmlx-gantt and we have a licence of your product dhtmlxScheduling Plus Pack.
Lately we had updated it to the latest version 7.1.13 (from 7.1.3). Now we noticed that we are not able to resize columns on the grid element in gantt view. I read through forum that this can be a case as we may have standard not pro edition.
I download the code source of 7.1.13 version from your public GitHub. Can you give me a help how to get the 7.1.13 source code in pro edition according to our license to have all the features as we had with 7.1.3?

Hello Pawel,
Please submit a support request regarding this issue, and we’ll provide the instructions to download the Pro version. You can find the instructions in the email with the license.