'PKIX path building failed'

Question

So, I am working on a project using Twilio API in Java and Spring Boot but I am getting this error.

"PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target"

Please, provide any help or any resource if available.

This is my Controller:

@PostMapping("/trigger-alert")
public String triggerAlert(@RequestBody String phoneNumbers, Model model) {
    try {
        String message = "Alert: Something happened!";
        smsService.sendBulkSms(phoneNumbers, message);
        model.addAttribute("message", "Alert triggered, SMS sent to multiple numbers!");
        model.addAttribute("phoneNumbers", phoneNumbers);
        return "success";
    }catch (Exception e){
        System.out.println(e.getMessage());
    }
    return "error";
}

And this is the Service this controller is using:

public SMSService() {
    Twilio.init(Account_SSID, Auth_TOKEN);
}

public void sendBulkSms(String phoneNumbers, String messageContext) {
    // Implement SMS sending logic here
    for (String splitPhoneNumber : splitPhoneNumbers(phoneNumbers)) {
        sendSMS(splitPhoneNumber, messageContext);
    }

}

private void sendSMS(String to, String userMessage){
    Message message = Message.creator(
        new PhoneNumber(to),
        new PhoneNumber(Twilio_PhNum),
        userMessage
    ).create();

    System.out.println("Sent Message to " + to + ": " + message.getSid());
}

public static ArrayList<String> splitPhoneNumbers(String phoneNumbersCommaSeparated) {
    // Trim the input string to remove any leading or trailing whitespace
    String trimmedInput = phoneNumbersCommaSeparated.trim();

    // Check if the input is empty
    if (trimmedInput.isEmpty()) {
        return new ArrayList<>(); // Return an empty ArrayList if input is empty
    }

    // Split the input string by commas
    String[] phoneNumbersArray = trimmedInput.split("\\s*,\\s*");

    // Convert the array to an ArrayList

    return new ArrayList<>(Arrays.asList(phoneNumbersArray));
}

tried few things but its not working.