Hello KrankedCLS,I also have this exact same issue with this website. I was wondering how did you create the cookie file (zzup.txt) and why you didn't specify a path in your command line ?
I tried to generate the .txt with export cookie add on firefox and specifying the path in the command line but I still get the error:

gallery-dl https://zzup.com/content/MTY1MTc1NQ==/2017_05_14_xl_bree_g/MQ==/index.html --cookies /home/myusername/Documents/cookies.txt --user-agent "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:130.0) Gecko/20100101 Firefox/130.0"
[zzup][warning] Cloudflare challenge
[zzup][error] HttpError: '403 Forbidden' for 'https://zzup.com//content/MTY1MTc1NQ==/2017_05_14_xl_bree_g/MQ==/index.html' 

I suspect something is wrong with the file.

P.S.: To answer your other question...the reason i didn't specify a path is because the cookies file is in the same folder as the executable and i'm not using a config file, i just been using a straight forward setup without issues until zz updated their site.

@KrankedCLS Thanks again for the help.

I changed the format export to Netscape then I copied/pasted the value field to cookies.txt but I still get the same error.

[zzup][warning] cookies: not enough values to unpack (expected 7, got 1)
[zzup][warning] Cloudflare challenge
[zzup][error] HttpError: '403 Forbidden' for 'https://zzup.com//content/MTY1MTc1NQ==/2017_05_14_xl_bree_g/MQ==/index.html'

Maybe I did something wrong ?

I found it strange because I also tried Export Cookies addon to directly export .txt file and the cookies works without error but I still get the error:

[zzup][warning] Cloudflare challenge
[zzup][error] HttpError: '403 Forbidden' for 'https://zzup.com//content/MTY1MTc1NQ==/2017_05_14_xl_bree_g/MQ==/index.html'

You are using the wrong copy paste method. What you have to do is click EXPORT at the top (i guess i wasn't clear enough, sorry!), you see that arrow pointing right?...that's the export option. It will export in the correct formatting. You should have 5 lines that relate to zzup. Not just one big line.

# Netscape HTTP Cookie File
# http://curl.haxx.se/rfc/cookie_spec.html
# This file was generated by EditThisCookie
.zzup.com	TRUE	/	TRUE	1757822735	cf_clearance	a bunch of characters here
.zzup.com	TRUE	/	FALSE	1726345720	count	5000
.zzup.com	TRUE	/	FALSE	1726345720	level_id	1
.zzup.com	TRUE	/	FALSE	1726345720	zzupid	41014
.zzup.com	TRUE	/	FALSE	1726345720	zzupuser	username

Also make sure you login to zzup and use that updated cookie....create an account if you don't have one, you should see your username at the bottom of the cookies.txt. Once you get it working, remember that you'll have to update the cookies when you get the error again.

The cookie are working great now , thank you ! I still had the issue with cloudflare challenge error but after a few searches I stumbled upon this thread mentioning that the user agent and the cookies you generated must match and now everything is working perfectly !

Awesome, glad you were able to finally get it to work.