When I went to Appearance on dashboard and then clicked on theme editor to update some files. However, when I tried to click 'update'. The error message
"Something went wrong. Your change may not have been saved. Please try again. There is also a chance that you may need to manually fix and upload the file over FTP." shows up.
I have tested every single plug-in. But, it doesn't seem to have anything to do with the plug-in. The theme was built by a previous developer hired before me. So, could it possibly have something to do with the ownership or permission set by the previous programmer. If so, am I still able to upload the file over FTP?
This Message comes from Wordpress, This option disabled by WordPress for preventing down the site because if who somebody edited themes while had a syntax error after saving code then he/she can not be edit codes again. So, he/she must resolve this issue with Host panel (cPanel or etc).
If you want to enable this option you can use below code in wp-config.php:
define( 'DISALLOW_FILE_MODS', false );
The best practice for edit themes is Git or FTP.