I want to add DHTMLX Scheduler (License url) on the website I am making, the website will provide a certain service for free (there will be other sources of profit, as premium features) to it’s users and I need the calendar to be used by the users to schedule and be notified about certain things concerning the website.

The DHTMLX Scheduler comes in 3 types of license: GNU GPL, Commercial License, Enterprise License Use in non-GPL project is not allowed in the GNU GPL licence which is what interests me cause it is the free to use licence.

Since my website is not released yet I have not taken time to search about licensing.

My website will use some algorithms in PHP for it’s main functionality(kinda like a closed api) and send the results to be handled by JS in the frontend. These PHP algorithms will not be open sourced.

So my question is can I use the free license(GNU GPL) of the scheduler on my project ?