Hi Ludwig --
That's a nice looking coin. I have tried to find an EXACT match in my database, but have not found an EXACT one. I'm nor sure your RIC number is correct. Here are the results of my search:
CONSTANTINVS -- for sure
Draped bust -- for sure
Sol standing left holding globe -- for sure
SOLI INVICTO COMITI inscription reverse -- for sure
BTR in exergue -- probably
F-T in field -- can't find this is my database, paired with the other 'for sure' items (there are plenty of T-F fields that match)
The closest I could find is pictured. Below is it's auction description. Your coin probably carries similar value, unless the F-T field makes it rare, but I don't know this.
Roma Numismatics Ltd > E-Sale 78 Auction date: 17 December 2020
Lot number: 1780
Price realized: 70 GBP (Approx. 94 USD / 78 EUR / 84 CHF)
Constantine I BI Nummus. Treveri, AD 310-313. IMP CONSTANTINVS AVG, laureate, draped and cuirassed bust to right / SOLI INVICTO COMITI, radiate Sol standing facing, head left, chlamys draped over left shoulder, holding globe and raising right hand; T-F across fields, PTR in exergue. RIC VI 871. 3.70g, 24mm, 6h.
Ex Dieter Alten Collection, purchased from Fritz Rudolf Künker GmbH & Co. KG, March 2009.
Estimate: 30 GBP
Hi again, Ludwig.
As they say in the movies ... we make a good team. Thanks for your efforts. Persistence pays off.
Trier was a big help.
(BTW, I invest $600 per year in the CoinArchivesPro database. It is a VERY useful numismatic tool for all coins, except US coins. Advertising revenue from the main CoinQuest web site offsets the $600.)
So the "R" is a rarity indicator. Got it. Don't quickly dismiss R4. It is probably correct. Here is an analysis of database search results.
"Constantine I" - returned 52083 coins
Add "Trier" - returned 3310 coins
Add "ae follis" - returned 1189 coins
Add "ric vii" - returned 251 coins
Add "158" - returned 4 coins
Looks good. However, none of the 4 coins returned by the "158" search match your coin. Instead, I looked through the 251 coin images for the "ric vii" search and found only 2 coins with an F-T field. But, both of the F-T coins have a different portrait of the emperor (pictured).
Summary: starting with 50000+ Constantine coins, yours is not in the database. R4 sounds right. I'd guess your coin would sell in the $200 to $300 US dollar range, perhaps more. Yay!
Consider contacting WildWinds. The picture of their coin looks like it came from the CoinArchivesPro database, even though I can't find it. That means the WildWinds coin was sold at auction. Tracking down the specific auction would help in determining value.