add_sms_provider.php

<?php
/*
* slug: smswoo_clicksend
* replace slug in the code
*/
add_filter( 'smswoo_sms_provider_array', 'smswoo_sms_provider_array', 10, 1 );
function smswoo_sms_provider_array( $settings ){
	$settings['smswoo_sms_provider']['options']['smswoo_clicksend'] = 'ClickSend';
	
	// add the settings to SMS section so you can retrive SMS cridential
	$settings['smswoo_clicksend_username'] = array(
		'title'		=> __( 'Clicksend API Username', 'trackship-for-woocommerce' ),
		'type'		=> 'text',
		'show'		=> true,
		'id'		=> 'smswoo_clicksend_username',
		'class'		=> 'smswoo_sms_provider smswoo_clicksend_sms_provider',
	);
	$settings['smswoo_clicksend_key'] = array(
		'title'		=> __( 'Clicksend API key', 'trackship-for-woocommerce' ),
		'type'		=> 'text',
		'show'		=> true,
		'id'		=> 'smswoo_clicksend_key',
		'class'		=> 'smswoo_sms_provider smswoo_clicksend_sms_provider',
	);

	//make sure to add slug in the class for sender phon number
	$settings['smswoo_sender_phone_number']['class'] = $settings['smswoo_sender_phone_number']['class'] . ' smswoo_clicksend_sms_provider ';
	
	return $settings;
}

/*
* Make sure that class name is same as slug
* slug: smswoo_clicksend
*/
if ( ! class_exists( 'smswoo_clicksend' ) ) {

	/**
	*
	* @class   smswoo_clicksend
	* @since   1.0
	*
	* Make sure that you extend the class smswoo_sms_gateway
	*
	*/
	class smswoo_clicksend extends smswoo_sms_gateway {
		
		private $_clicksend_authkey;
		
		/**
		* Constructor
		*
		* @since   1.0
		* @return  void
		*/
		public function __construct() {
			
			// get cridential from settings fields
			$this->_clicksend_username    = get_option( 'smswoo_clicksend_username' );
			$this->_clicksend_key    = get_option( 'smswoo_clicksend_key' );

			parent::__construct();

		}
		
		/**
		* Send SMS
		*
		* @since   1.0
		*
		* @param   $to_phone     string
		* @param   $message      string
		* @param   $country_code string
		*
		* @return  void
		* @throws  Exception for WP HTTP API error, no response, HTTP status code is not 201 or if HTTP status code not set
		*/
		public function send( $to_phone, $message, $country_code ) {

			if ( '' != $this->_from_asid ) {
				$from = $this->_from_asid;
			} else {
				$from = $this->_from_number;
			}
			
			$type = empty( apply_filters( 'smswoo_additional_charsets', get_option( 'smswoo_active_charsets', array() ) ) ) ? 'english' : 'unicode';	
			
			$body = array(
				'messages' => array(
					array(
						'to'		=> $to_phone,
						'source'	=> "smswoo",
						'body'		=> $message,
					),
				),
			);
			
			$args = array(
				'body'    => wp_json_encode( $body ),
				'headers' => array(
					'Authorization' => "Basic " . base64_encode( $this->_clicksend_username.":".$this->_clicksend_key ),
					'Content-Type' => 'application/json',
				),
			);
			
			$url = 'https://rest.clicksend.com/v3/sms/send';
			
			$response = wp_safe_remote_post( $url, $args);
			
			if ( is_wp_error( $response ) ) {
				throw new Exception( $response->get_error_message() );
			}

			$this->_log[] = $response;

			// Check for proper response / body
			if ( ! isset( $response['response'] ) || ! isset( $response['body'] ) ) {
				throw new Exception( __( 'No answer', 'trackship-for-woocommerce' ) );
			}
			
			$result = json_decode( $response['body'], true );
			if ( $result['response_code'] != 'SUCCESS' ) {
				
				throw new Exception( sprintf( __( 'An error has occurred: %s', 'trackship-for-woocommerce' ), $result['response_msg'] ) );

			}

			if ( $result[ 'data' ][ 'messages' ][0]['status'] != 'SUCCESS' ) {
				
				throw new Exception( sprintf( __( 'An error has occurred: %s', 'trackship-for-woocommerce' ), $result[ 'data' ][ 'messages' ][0]['status'] ) );
				
			}
			
			return;
		}
		
		/**
		 * Send SMS
		 *
		 * @since   1.0
		 *
		 * @param   $to_phone     string
		 *
		 * @return  void
		 * @throws  Exception for WP HTTP API error, no response, HTTP status code is not 201 or if HTTP status code not set
		 */
		public function validate_number( $to_phone ) {			
			throw new Exception( sprintf( __( 'An error has occurred: Clicksend is not supported for phone number validation on checkout, Please contact support', 'trackship-for-woocommerce' ) ) );
		}
	}
}