You can contact Customer Support through the Fantasy Grounds Help Center:
Tell us whether or not you are using Fantasy Grounds (Classic) or Fantasy Grounds Unity
Tell us whether you purchased on Steam, DMsGuild, or on fantasygrounds.com
What Operating System are you using (Windows, Mac, Linux) and which version # if you have it
What is your username on fantasygrounds.com
If you had an error, what steps did you take before you received the error.
Screenshots of any errors you are received are helpful.
If the Fantasy Grounds Help Center form isn’t working properly, you can also contact Support by email.
Email us at firstname.lastname@example.org