503 Error while trying to send SMS with Twilio - php

Question

I´m using Twilio PHP API to send mass sms to my customers.
Problem is that i can only send like 80st SMS and then i got a server error:
Failed to load resource: the server responded with a status of 503
(Backend fetch failed)
Well i think this might be the error.
Because i get no success echo echo "Sent message to $name and in the twilio SMS log i can only see that 80 SMS of 200 has been sent.
What can cause this error?
foreach ($usrs as $number => $name) {
try{
$sms = $client->account->messages->create(
// the number we are sending to - Any phone number
$number,
array(
// Step 6: Change the 'From' number below to be a valid Twilio number
'from' => "xxxxxxxxxxx",
// the sms body
'body' => "Hey $name. $text"
)
);
// Display a confirmation message on the screen
echo "Sent message to $name <br>";
}
catch (TwilioException $e) {
die( $e->getCode() . ' : ' . $e->getMessage() );
}
}

Answer 1

Twilio developer evangelist here.
Twilio has a limit of 100 concurrent API requests and will only send 1 message a second. As Ahmed suggested in the comments, I recommend you add a delay between calls to the API if you are sending more than 100 messages.
edit
Adds sleep(1) for each message. This will make the page delay a second after sending each message.
foreach ($usrs as $number => $name) {
try{
$sms = $client->account->messages->create(
// the number we are sending to - Any phone number
$number,
array(
// Step 6: Change the 'From' number below to be a valid Twilio number
'from' => "xxxxxxxxxxx",
// the sms body
'body' => "Hey $name. $text"
)
);
// Display a confirmation message on the screen
echo "Sent message to $name <br>";
sleep(1);
}
catch (TwilioException $e) {
die( $e->getCode() . ' : ' . $e->getMessage() );
}
}