Insert a Variable of String into an array - php

Question

I'm using a Sendinblue SMTP into my PHP project and I want to send transactionals emails to a dynamic list of emails, the problem is that I have a syntax error when I'm using a variable instead a string. For example, this code works great:
include 'Mailin.php';
$mailin = new Mailin('senders#sender.com', 'key');
$mailin->
addTo(
array(
'email1#email.com' => '', 'email2#email.com' => '', 'email3#email.com' => ''
)
)->
setFrom('sender#sender.com', 'Test')->
setReplyTo('sender#sender.com', 'Test')->
setSubject('Example')->
setText('Test')->
setHtml($htmlContent);
$res = $mailin->send();
print_r($res);
But if I use a variable instead the Strings in "addTo Array" it shows syntax error, for example:
$customers = '';
foreach ($clientes as $customer) {
for ($i=1; $i < 41; $i++) {
if ($customer['email'.$i] != "" or $customer['email'.$i] != NULL) {
$customers .= "'".$customer['email'.$i]. "' => '', " ; //for each customer's email add the email in " 'email#email.com' => '', " format
}
}
}
$customers = substr($customers, 0, -2); //removes last space and comma of the String
include 'Mailin.php';
$mailin = new Mailin('senders#sender.com', 'key');
$mailin->
addTo(
array(
$customers
)
)->
setFrom('sender#sender.com', 'Test')->
setReplyTo('sender#sender.com', 'Test')->
setSubject('Example')->
setText('Test')->
setHtml($htmlContent);
$res = $mailin->send();
print_r($res);
If I use the Print_r($customers) function it shows the exact string that I used in my first example, even if I use the code:
$text = "'email1#email.com' => '', 'email2#email.com' => '', 'email3#email.com' => ''";
if ($customers == $text) {
print_r("Yes");
}else{
print_r("No");
}
The result is "Yes", but when I use the variable in
addTo(
array(
$customers
)
)->
shows an error, but if I use the string directly the email is sent
addTo(
array(
'email1#email.com' => '', 'email2#email.com' => '', 'email3#email.com' => ''
)
)->
And I don't know why it shows error if the $customers variable has the string that is needed.
Do you know how to use the variable with the emails that I need to send?

Answer 1

You don't build an array by concatenating strings with => in them. To create an element in an associative array, just assign to that array index.
$customers = [];
foreach ($customers as $customer) {
for ($i = 1; $i < 41; $i++) {
if (!empty($customer["email" . $i])) {
$customers[$customer["email" . $i]] = "";
}
}
}
include 'Mailin.php';
$mailin = new Mailin('senders#sender.com', 'key');
$mailin->
addTo($customers)->
...
Also, see Why non-equality check of one variable against many values always returns true? for why you should have used && rather than || when you were skipping empty emails (which I've simplified by using !empty()).