command c expects followed by text error in Mac

You received error from the sed command in Mac, because the argument in mac is different.
If you type in Mac terminal, you may receive error like this

Justins-MacBook-Pro:2 juzhax$ sed -i 's/old_text/new_text/g' example.txt
sed: 1: "config.php": command c expects \ followed by text

The first argument should be the extension of the backup file. The correct way is

Justins-MacBook-Pro:2 juzhax$ sed -i '.bak' 's/old_text/new_text/g' example.txt

or

Justins-MacBook-Pro:2 juzhax$ sed -i '.original' 's/old_text/new_text/g' example.txt

If you don’t want any backup file, you can do like this.

Justins-MacBook-Pro:2 juzhax$ sed -i '' 's/old_text/new_text/g' example.txt