Critical fail on website
After updating the company site to 5.5 – I made a backup before – I started getting critical theme errors.
The site is https://credence.co.uk – you can see the error message here.
It says there is a fatal error: call to undefined function in header.php. If I remove header.php, the site loads, but obviously, it looks messed up as there is no header code.
Any ideas why updating to 5.5 messed up my theme? And why reverting to backups makes no difference?
Or if anyone that knows PHP better than me can help me fix the header file, I would be so thankful.