Payment.cs

public interface IPaymentService
{
    Task<string> ChargeAsync(decimal amount, string token);
}

public class StripePaymentService : IPaymentService
{
    public async Task<string> ChargeAsync(decimal amount, string token)
    {
        var service = new ChargeService();

        var charge = await service.CreateAsync(new ChargeCreateOptions
        {
            Amount = (long)(amount * 100),
            Currency = "usd",
            Source = token
        });

        return charge.Id;
    }
}

public class ProcessPayment
{
    public record Command(decimal Amount, string Token);

    public class Handler
    {
        private readonly IPaymentService _paymentService;

        public Handler(IPaymentService paymentService)
        {
            _paymentService = paymentService;
        }

        public async Task Handle(Command command)
        {
            var paymentId = await _paymentService.ChargeAsync(command.Amount, command.Token);

            // save result, publish event, etc.
        }
    }
}