You could not have had a better start. Great coin, from one of the most reliable and knowledgeable dealers out there, and a nice guy to boot. Here's my version of your coin, and my write-up. So the year is 350 A.D. There are two Roman emperors: Constantius II in the East and Constans in the West, both sons of Constantine the Great. Magnentius, a former imperial guard commander, arose in the West and usurped the rule of Constans, who was soon trapped and killed near the Pyrenees. Magnentius had to act fast to solidify his base of power because rivals in the West (such as Vetranio) were gathering troops, and soon Constantius would arrive from the East to avenge his brother. Perhaps as a genuine gesture of piety, or perhaps as a crass means of rallying the support of the Christian faction, Magnentius had this coin struck featuring a large Chi-Rho monogram. (It also features a portrait that makes Magnentius look like Conway Twitty.) While the Chi-Rho had been featured in small details of Constantinian coinage, never had it held such prominence. The iconographical message is startling: Magnentius, not the sons of Constantine, was the true heir to Christian Empire. After all, his Chi-Rho was bigger than their Chi-Rho. Sadly for Magnentius, his Chi-Rho couldn’t save him, at least not physically. He was soundly defeated by Constantius at the Battle of Mursa Major in Croatia in 351. (Magnentius personally led his troops into battle; Constantius left the battle to pray.) Magnentius’s forces suffered a final defeat in southern France at the Battle of Mons Seleucus, after which Magnentius died the “Roman death” by falling on his sword in 353.
There's nothing wrong with doubting authenticity, not just in terms of whether it's fake or not, but whether it has been attributed correctly. There are fakes out there, some that even trick dealers, although this should be much less likely through VCoins than eBay (but not impossible). I'm relatively new to this too and I might be wrong, but I haven't found fakes to be an issue when buying through reputable dealers (not eBay). But a few times I've bought coins that turned out to be wrongly attributed. On a couple of occasions they didn't even get the ruler correct. The wrong attribution could change the value of the coin quite significantly, so it's worth checking yourself, or if that fails, on here. Having said that, researching the coin is a huge part of the fun of collecting. Once you've done that, quite often you'll answer any questions yourself. (And find you now have a long wish list of other coins you want).
Welcome, @BRIAN HARRIS . Great first coin. I have an XP with Poemenius: RI Poemenius in name of Constantius II summer 353 Trier XP RIC VIII Trier 332 RARE Ex: @seth77
That's such a good history of the coin! Where did you get it? That's interesting enough to make me consider diving into ancients if I can get that history to back the coin!
@BRIAN HARRIS , Welcome. If you are interested in coins with Christian symbols, this site might be of interest to you. http://augustuscoins.com/ed/Christian/ChristianSymbols.html This is @Valentinian 's site and has an enormous amount of good information. For a broader look, the high level index is here http://augustuscoins.com/ed/
Some of my Poemenius revolt types are also courtesy of @Victor_Clark @Alegandron yours I think is courtesy of Roy Flora.
@BRIAN HARRIS That is a lovely first coin...congrats. You did the one thing that many people new to the hobby do not do. You bought from a trusted source. You cannot do any better than buying from Victor. He is knowledgeable, trustworthy and kind.