$conn $=$ mysqli$\_$connect$($$servername, $username, $password, $dbname$)$;

$//$

if $(!$$conn$)\{$

die$("$Connection failed: $".$ mysqli$\_$connect$\_$error$())$;

$\}$

if $($$$\_$SERVER$["$REQUEST$\_$METHOD"$]==$ "POST"$)\{$

$//$

if $(!$empty$($$$\_$POST$["$name$"])$ && $!$empty$($$$\_$POST$["$date$\_$of$\_$birth"$])$ && $!$empty$($$$\_$POST$["$phone$"])$ && $!$empty$($$$\_$POST$["$center$\_$name"$])$ && $!$empty$($$$\_$POST$["$reservation$\_$date"$]))\{$

$//$

$name $=$ $$\_$POST$["$name$"]$;

$date$\_$of$\_$birth $=$ $$\_$POST$["$date$\_$of$\_$birth"$]$;

$phone $=$ $$\_$POST$["$phone$"]$;

$center$\_$name $=$ $$\_$POST$["$center$\_$name"$]$;

$reservation$\_$date $=$ $$\_$POST$["$reservation$\_$date"$]$;

$//$ ID $$

$center$\_$id $=$ null;

$stmt $=$ $conn$->$prepare$("$SELECT center$\_$id FROM P$\_$Blood$\_$Center WHERE center$\_$name $=?")$;

if $(!$$stmt$)\{$

die$("$Prepare failed: $".$ $conn$->$error$)$;

$\}$

$stmt$->$bind$\_$param$("$s$",$ $center$\_$name$)$;

$stmt$->$execute$()$;

$stmt$->$bind$\_$result$($$center$\_$id$)$;

$stmt$->$fetch$()$;

$stmt$->$close$()$;

if $($$center$\_$id $===$ null$)\{$

die$("$Center ID not found"$)$;

$\}$

$//$ ID $$

$donor$\_$id $=$ getDonor$\_$id$($$conn, $phone$)$;

$//$ ID $$

if $($$donor$\_$id$)\{$

$//$ ID$$

insertP$\_$Donation$($$conn, $donor$\_$id$,$ $center$\_$id$,$ $reservation$\_$date$)$;

$\}$ else $\{$

$//$ ID$$

$donor$\_$id $=$ insertP$\_$Donor$($$conn, $name, $date$\_$of$\_$birth, $phone$)$;

if $($$donor$\_$id$)\{$

insertP$\_$Donation$($$conn, $donor$\_$id$,$ $center$\_$id$,$ $reservation$\_$date$)$;

$\}$ else $\{$

echo "alert$(\text{'}$Error adding new donor'$)$;$"$;

$\}$

$\}$

$\}$ else $\{$

echo "alert$(\text{'}$All fields must be filled out'$)$;$"$;

$\}$

$\}$

$stmt$->$close$()$;

$//$

function insertP$\_$Donation$($$conn, $donor$\_$id$,$ $center$\_$id$,$ $reservation$\_$date$)\{$

$stmt $=$ $conn$->$prepare$("$INSERT INTO P$\_$Donation $($center$\_$id$,$ reservation$\_$date, donor$\_$id$)$ VALUES $(?,?,?)")$;

if $(!$$stmt$)\{$

die$("$Prepare failed: $".$ $conn$->$error$)$;

$\}$

$stmt$->$bind$\_$param$("$iss$",$ $center$\_$id$,$ $reservation$\_$date, $donor$\_$id$)$;

if $($$stmt$->$execute$())\{$

echo "alert$(\text{'}$Data Inserted Successfully'$)$;$"$;

$\}$ else $\{$

echo "alert$(\text{'}$Error Inserting Data: $".$ $stmt$->$error $."\text{'})$;$"$;

$\}$

$stmt$->$close$()$;

$\}$

function insertP$\_$Donor$($$conn, $name, $date$\_$of$\_$birth, $phone$)\{$

$stmt $=$ $conn$->$prepare$("$INSERT INTO P$\_$Donor $($name$,$ date$\_$of$\_$birth, phone$)$ VALUES $(?,?,?)")$;

if $(!$$stmt$)\{$

die$("$Prepare failed: $".$ $conn$->$error$)$;

$\}$

$stmt$->$bind$\_$param$("$sss$",$ $name, $date$\_$of$\_$birth, $phone$)$;

if $($$stmt$->$execute$())\{$

return $stmt$->$insert$\_$id;

$\}$ else $\{$

echo "alert$(\text{'}$Error Inserting Donor: $".$ $stmt$->$error $."\text{'})$;$"$;

return null;

$\}$

$stmt$->$close$()$;

$\}$

function getDonor$\_$id$($$conn, $phone$)\{$

$stmt $=$ $conn$->$prepare$("$SELECT donor$\_$id FROM P$\_$Donor WHERE phone $=?")$;

if $(!$$stmt$)\{$

die$("$Prepare failed: $".$ $conn$->$error$)$;

$\}$

$stmt$->$bind$\_$param$("$s$",$ $phone$)$;

$stmt$->$execute$()$;

$stmt$->$bind$\_$result$($$donor$\_$id$)$;

$stmt$->$fetch$()$;

$stmt$->$close$()$;

return $donor$\_$id;

$\}$

I omitted some codes including connection info. $($connection doesn't have any problems$)$ I tried to insert data in DB when form in this html file registered. But nothing happens including error text. What's the matter?