Support intro
Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 29.0.5): 30.0.0
Operating system and version (eg, Ubuntu 24.04): Ubuntu 22.04 LTS
Apache or nginx version (eg, Apache 2.4.25): Apache
PHP version (eg, 8.3): 8.3
The issue you are facing:
Tried upgrading to PHP 8.3 as php 8.1.2 is depricated as per the instructions of Nextcloud 30, and after a bit, I’m now getting error 503 Service unavailable
Is this the first time you’ve seen this error? (Y/N): Y
I do not know what I did wrong, nor how to fix it. I was trying to get Nextcloud to use PHP 8.3, but now it’s not running at all, and I’m unsure what I’ve done wrong.
Edit: Here’s the output of…
php -v:
PHP 8.3.12 (cli) (built: Sep 27 2024 03:53:05) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.12, Copyright (c) Zend Technologies
with Zend OPcache v8.3.12, Copyright (c), by Zend Technologies
php -m
[PHP Modules]
bcmath
bz2
calendar
Core
ctype
curl
date
dom
exif
FFI
fileinfo
filter
ftp
gd
gettext
gmp
hash
iconv
igbinary
imap
intl
json
ldap
libsmbclient
libxml
mbstring
memcached
msgpack
mysqli
mysqlnd
openssl
pcntl
pcre
PDO
pdo_mysql
pdo_pgsql
pgsql
Phar
posix
random
readline
Reflection
session
shmop
SimpleXML
smbclient
soap
sockets
sodium
SPL
standard
sysvmsg
sysvsem
sysvshm
tokenizer
xml
xmlreader
xmlwriter
xsl
Zend OPcache
zip
zlib