is Frontier website down ? Have been trying for hours
 

keep getting 403 Error

It's working fine for me, but apparently it's not just you having an issue.
https://downforeveryoneorjustme.com/flyfrontier.com

can now get to

https://flyfrontier.custhelp.com/

but not Frontier home page

As an overseas customer, I am receiving this error all the time. Looks like they are simply blocking any IP adress that's not located in the US.

Want to book a new flight? - 403 Forbidden

Want to log in to my Elite 100K account and have a look at the expiration date? - 403 Forbidden

Want to cancel Discount Den membership as written in the E-Mail I received? - 403 Forbidden

It is extremly annoying and one of the reasons why I will avoid doing business with Frontier in the future.

I'm based in the US. I don't get any 403 errors, but any time I try to book a ticket on the Frontier site I get forwarded to a site titled 'ShieldSquare Block' that says:

This only happens on my laptop, not on my phone. My guess is they identified my device as accessing the Frontier website an unusually high number of times so they blocked it. Which of course is not because I'm doing anything nefarious, but because I fly with them all the time. Tsk tsk.

Try using a US-based VPN service and an incognito/private browsing window. That should do the trick.
Another option is to use the Frontier app which may work better.