SendGrid dynamic template contains empty data - .NET Core

I am trying to send an email with a specific dynamic template and data. Email is successfully sent but contains empty data. The handle method is part of Azure Function. Recently I've changed Newtonsoft JSON to System.Text.Json and maybe this causes some problems.

Email:

SendGrid dynamic template configuration:

C# Code:

        public async Task Handle(SendEmailCommand command)
        {
            var client = new SendGridClient(emailConfig.SendGridApiKey);
            var msg = new SendGridMessage();

            msg.SetFrom(new EmailAddress(emailConfig.Sender));
            msg.AddTo(new EmailAddress(command.To));
            msg.SetTemplateId(command.SendGridTemplateId);

            if (command.SendGridDynamicTemplateData != null)
            {
                var templateData = new TemplateData();

                command.SendGridDynamicTemplateData.TryGetValue("topic", out var topic);
                command.SendGridDynamicTemplateData.TryGetValue("email", out var email);
                command.SendGridDynamicTemplateData.TryGetValue("name", out var name);
                command.SendGridDynamicTemplateData.TryGetValue("message", out var message);

                templateData.Topic = topic.ToString();
                templateData.Email = email.ToString();
                templateData.Name = name.ToString();
                templateData.Message = message.ToString();

                msg.SetTemplateData(templateData);
            }

            await client.SendEmailAsync(msg);
        }

        private class TemplateData
        {
            [JsonPropertyName("topic")]
            public string Topic { get; set; }

            [JsonPropertyName("email")]
            public string Email { get; set; }

            [JsonPropertyName("name")]
            public string Name { get; set; }

            [JsonPropertyName("message")]
            public string Message { get; set; }
        }

Am I doing something wrong?