how to write a batch apex to get notification when a managed package is getting expired soon and also we have to send a email notification when package is about to expire , I have written a batch but it is working as expected , can you help me with the logic

i was expecting that the batch should a email notification but it was not happening as excepted and instead it was giving me a error (First_Exception:Invalid token[)

This is the class

global class PackageExpiryNotificationBatch implements Database.Batchable<SObject>, Database.Stateful, Schedulable, Database.AllowsCallouts {
    global Database.QueryLocator start(Database.BatchableContext BC) {
        String query = 'SELECT Id, Name, Expiration_Date__c FROM Package__c WHERE Expiration_Date__c <= :Date.today().addMonths(3)';
        return Database.getQueryLocator(query);
    }

    global void execute(Database.BatchableContext BC, List<Package__c> scope) {
        List<Messaging.SingleEmailMessage> emails = new List<Messaging.SingleEmailMessage>();
        List<Package__c> packagesExpiring = new List<Package__c>();

        // Fetch recipient email from custom setting
        NotificationSettings__c settings = NotificationSettings__c.getValues('Default');
        String recipientEmail = settings != null ? settings.RecipientEmail__c : '[email protected]';



        for (Package__c pkg : scope) {
            // Add to list for Mattermost notification
            packagesExpiring.add(pkg);

            // Create email notification
            Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
            email.setToAddresses(new String[] {recipientEmail});
            email.setSubject('Package Expiry Notification');
            email.setPlainTextBody('The package ' + pkg.Name + ' is expiring on ' + pkg.Expiration_Date__c.format() + '.');
            emails.add(email);
        }

        // Send all emails
        if (!emails.isEmpty()) {
            Messaging.sendEmail(emails);
        }

        // Send Mattermost notification
        sendMattermostNotification(packagesExpiring, recipientEmail);
    }

    global void finish(Database.BatchableContext BC) {
        // Log or perform any necessary post-batch operations
    }

    global void execute(SchedulableContext SC) {
        Database.executeBatch(new PackageExpiryNotificationBatch());
    }

    // Method to send Mattermost notification
    private void sendMattermostNotification(List<Package__c> packagesExpiring, String recipientEmail) {
        String mattermostWebhookUrl = 'https://mattermost.example.com/hooks/your-webhook-url';
        String message = 'The following packages are expiring within the next 3 months:n';

        if (packagesExpiring.isEmpty()) {
            message += 'No packages are expiring within the next 3 months.';
        } else {
            for (Package__c pkg : packagesExpiring) {
                message += '- ' + pkg.Name + ' expiring on ' + pkg.Expiration_Date__c.format() + 'n';
            }
        }

        HttpRequest req = new HttpRequest();
        req.setEndpoint(mattermostWebhookUrl);
        req.setMethod('POST');
        req.setHeader('Content-Type', 'application/json');
        req.setBody('{"text":"' + message + '"}');

        Http http = new Http();
        HttpResponse res = http.send(req);

        if (res.getStatusCode() != 200) {
            System.debug('Failed to send Mattermost notification: ' + res.getStatus());
        }
    }
}