Hey @dd214
you should check the PHP.ini you created for i-doit.
The path is like /etc/php/7.x/mods-available/i-doit.ini
Where the 7.X is the used PHP Version.
If the file does not exist, create one.
See here https://kb.i-doit.com/pages/viewpage.action?pageId=36864037#DebianGNU/Linux-PHP