What is wrong with this code?

Question

I made this php program to get input from a html form and do some work with it (you'll understand when you look at the code).
The problem is when I input some text separated by a comma (,) in the text input of the html form, it shows the following error :
Pharse error : syntax error, unexpected 'echo' (T_ECHO) in C:\xampp\htdocs\handler\handler.php on line 15

https://code.sololearn.com/wN1ahSGZhsB5/?ref=app