Custum variables not parsed

[laslingerland]

I have created a template (6675577) in Mailjet and I use it to send transactional emails from my web application. Now the template is used, but the variables that I send to it, aren't parsed. The received email does show the unsubscribe message with parsed variables, but the First Name, Password and LoginUrl aren't parsed at all. I have tried the {{var:}} syntax, but it breaks the template and emails using it are blocked. The Nuget packages is strongly typed here, so I must use Dictionary<string, object>.

This message seems to be a duplicate of #78, but there it was closed because of inactivity and I simply can't get it to work. Not with Google, not with Copilot, simply not.

public class MailjetEmailService(ISecretProvider secretProvider, IConfiguration configuration) : IEmailService
{
    public async Task SendWelcomeEmailAsync(User user, string password)
    {
        const string subject = "Welcome";
        
        if (!long.TryParse(configuration["Mailjet:Templates:Welcome"], out var templateId))
        {
            throw new InvalidCastException("Invalid Mailjet TemplateID");
        }

        var frontendUrl = configuration["Frontend:Url"];
        if (frontendUrl == null)
        {
            throw new MissingAppSettingException("Frontend:Url");
        }
        
        var variables = new Dictionary<string, object>
        {
            {"FIRSTNAME", user.FirstName},
            {"PASSWORD", password},
            {"LOGINURL", frontendUrl}
        };

        await SendEmailAsync(user.Email, user.FullName, subject, templateId, variables);
    }
    
    private async Task SendEmailAsync(string to, string toName, string subject, long templateId, IDictionary<string, object> variables)
    {
        var apiKey = secretProvider.GetSecret("MailjetApiKey");
        var secretKey = secretProvider.GetSecret("MailjetSecretKey");
        
        var client = new MailjetClient(apiKey, secretKey);

        var email = new TransactionalEmailBuilder()
            .WithFrom(new SendContact("from@address.com", "FromName"))
            .WithSubject(subject)
            .WithTemplateId(templateId)
            .WithTemplateLanguage(true)
            .WithVariables(variables)
            .WithTo(new SendContact(to, toName))
            .Build();

        var response = await client.SendTransactionalEmailAsync(email);

        if (response.Messages.Length == 1)
        {
            Log.Information("Email sent with subject {Subject}", subject);
        }
        else
        {
            Log.Warning("Failed to send email with subject {Subject}", subject);
        }
    }
}