array_splice($lines, ($line_id + 1) + $offset, 0, explode("\n", $add));
This line i facing error and i have upgrade version 7 to 7.3 now facing this error
>Solution :
This is a feature introduced in 7.1 this means that a variable passed is non numeric in an aritmetic operation you can cast the value To be sure. in your code i suspect line_id or offset you can use (int).