Not Constantine rather a commemorative for Claudius II Gothicus cca. 270-271. Needs reverse too for proper id.
Online sources say international numismatic bureau is a scam. There's also an older topic to be found on this board.
Btw most collectors of ancients do not slab their coins. There are exceptions but slabbing is not looked upon in a kindly fashion by many members here. To know why just do a search for slabs on the ancients section.
As everybody else pointed out, this is a postumous issue of Claudius II "Gothicus." We would need to see the reverse to give a full ID, but these are generally very common. The slab should be regarded an attempt to fool buyers into thinking that it is more valuable. Just for comparison: Here is my own example, which is in much better condition. I paid $6, which was a bargain – the coin is maybe worth $10 on a very good day. Claudius II Gothicus (postumous), Roman Empire, BI antoninian, 270 AD, Rome or Mediolanum mint. Obv: DIVO CLAVDIO; head of Claudius Gothicus, radiate, r. Obv: CONSECRATIO; altar. 23.5mm, 2.84g. Ref: RIC V Claudius Gothicus 261 or 262.