Telesign(SMS API) Rest API sample code by using Customer ID and API key

public static String phoneVerification(String phone,String OTP){        
        HttpRequest request = new HttpRequest(); 
        HttpResponse response = new HttpResponse();  
        Http http = new Http();
        Blob beforeblob = Blob.valueOf('B76-954-84B073909FBE:bsLZCUHJWWqYEniMHEVvph8A+dKxa+K7zLooag==');
        
        string paramvalue = EncodingUtil.base64Encode(beforeblob);
        request.setEndpoint('https://rest-api.telesign.com/v1/messaging');
        request.setHeader('Authorization','Basic '+paramvalue);          
        request.setHeader('Content-Type','application/x-www-form-urlencoded'); 
        request.setMethod('POST');
        String msg = 'message=test msg';
        request.setBody(msg+'&message_type=OTP&phone_number='+phone);        
        if(!Test.isRunningTest()){
            response = http.send(request); 
        }  map<string,string> responseData  = (Map<String, String>)JSON.deserialize(response.getBody(), Map<String, String>.class);
          system.debug(responseData.get('Status'));
        return response.getBody(); 
    }