Help HELP PROGRAMING

[genshin_mica]

$user_input = readline("ASK: ")"\n";
function payload($user_input){
$payload = '{
"prompt": "'.$user_input.'",
}';
}

How can i get the user log input and put into function payload like this.

$user_input = readline("ASK: HELLOW")."\n";
function payload($user_input){
$payload = '{
"prompt": "HELLOW"\n'.$user_input.'",
}';
And so on, until the user stop prompt.