Access denied. How do you know what a variable is passing?

Question

PHP

When sending a test message, it gives the error "+3712995****: {"error":"access denied"}" . API key entered correctly.
How can I find out what the sms_service_id variable sends?
The code:

return file_get_contents_curl("https://app.sms.by/api/v1/sendQuickSMS?token=".$settings["sms_service_id"]."&message=".urlencode($text)."&phone=".$phone_to);

Function:

unction sms($phone_to="",$text=""){
   global $settings, $config;

   if($settings["sms_service_pass"]){
      $settings["sms_service_pass"] = decrypt($settings["sms_service_pass"]);
   }

   if($settings["sms_service_id"]){
      $settings["sms_service_id"] = decrypt($settings["sms_service_id"]);
   }

The form itself says:

value="<?php echo decrypt($settings["sms_service_id"]);

and the correct API is displayed there.