Paypal Processing - Need to grab TransactionId, CorrelationId and TimeStamp - asp.net

Question

Current Project:
ASP.NET 4.5.2
MVC 5
PayPal API
I am using this example to build myself a PayPal transaction (and yes, my code is virtually identical), as I do not know of any other method that will return the three values in the title.
My main problem is that, the example I am utilizing is much more concise and compact than the one I used for a much older Web Forms application, and as such, I am unsure as to where or even how to grab the three values I need.
My initial thought was to do so right after the ACK, and indeed I was able to obtain the CorrelationId as well as the TimeStamp, but because this was prior to the user being carted off to PayPal’s site (sandbox in this case -- see the return new PayPalRedirect contained within the if), the TransactionId was blank. And in this example, PayPal explicitly redirects the user to a Success page without returning to the Action that sent the user to PayPal in the first place, and I am not seeing any GET values in the URL at all aside from the Token and the PayerId, much less ones that could provide me with the TransactionId.
Suggestions?
I have also looked at the following examples:
For ASP.NET Core, was unsure how to adapt to my current project particularly due to appsettings.json, but it looked quite well done. I really liked how the values were rolled up in lists.
For MVC 4, but I couldn’t find where ACK was being used to determine success or successwithwarning so I couldn’t hook into that.
I have also found the PayPal content to be like trying to drink from a fire hose at full blast -- not only was the content was hopelessly outdated (Web Forms code, FTW!) but there was also so many different examples it would have taken me days to determine which one was most appropriate to use.
Any assistance would be greatly appreciated.
Edit: my initial attempt at modifying the linked code has this portion:
values = Submit(values);
var ack = values["ACK"].ToLower();
if(ack == "success" || ack == "successwithwarning") {
using(_db = new ApplicationDbContext()) {
var updateOrder = await _db.Orders.FirstOrDefaultAsync(x => x.OrderId == order.OrderId);
if(updateOrder != null) {
updateOrder.OrderProcessed = false;
updateOrder.PayPalCorrelationId = values["CORRELATIONID"];
updateOrder.PayPalTransactionId = values["TRANSACTIONID"];
updateOrder.PayPalTimeStamp = values["TIMESTAMP"];
updateOrder.IPAddress = HttpContext.Current.Request.UserHostAddress;
_db.Entry(updateOrder).State = EntityState.Modified;
await _db.SaveChangesAsync();
}
}
return new PayPalRedirect {
Token = values["TOKEN"],
Url = $"https://{PayPalSettings.CgiDomain}/cgi-bin/webscr?cmd=_express-checkout&token={values["TOKEN"]}"
};
}
Everything within and including the using() is my added content. As I mentioned, the CorrelationId and the TimeStamp come through just fine, but I have yet to successfully obtain the TransactionId.
Edit 2:
More problems -- the transactions that are “successful” through the sandbox site (the ReturnUrl is getting called) aren’t reflecting properly on my Facilitator and Buyer accounts, even when I do payments straight from the buyer’s PayPal account (not using the Credit Card). I know I am supposed to see transactions in the Buyer’s account, either through the overall Dev account (Accounts -> Profile -> balance or Accounts -> Notifications) or through the Buyer’s account in the sandbox front end. And yet -- multiple transactions returning me to the ReturnUrl path, and yet no transactions in either.
Edit 3:
Okay, this is really, really weird. I have gone over all settings with a fine-toothed comb, and intentionally introduced errors to see where things should crap out. It turns out that the entire process goes swimmingly - except nothing shows up in my notifications and no amounts get moved between my different accounts (Facilitator and Buyer). It’s like all my transactions are going into /dev/null, yet the process is successful.
Edit 4: A hint!
In the sandbox, where Buyer accepts the transaction, there is a small note, “You will be able to review the transaction before completing it” or something like that -- suggesting that an additional page is not coming up and that the user is being uncerimoniously dumped back to the success page. Why the success page? No clue. But it’s happening.

Answer 1

It sounds like you are only doing the first part of the process.
Express Checkout consists of 3 API calls:
SetExpressCheckout
GetExpressCheckoutDetails
DoExpressCheckoutPayment
SEC generates a token, and then you redirect to PayPal where the user signs in and reviews the transactions before agreeing to pay.
They are then sent to the ReturnURL included in your SEC request, and this is where you'll call GECD in order to obtain all the buyer details that are now available since they signed in.
Using that data you can complete the final DECP request, which is what finalizes the procedure. No money is actually processed until this final call is completed successfully.