The coin is genuine. The "seam" people are pointing to is just a reflection of light bouncing off of the background and onto the edge. This is frequently seen in most coin photos where the coin is sitting on a somewhat bright or reflective surface and honestly it should never be confused for an actual seam. As mentioned, this is likely Price 2090, which Price dated to 325-323 BC. Looks like Thompson dated it to the same period, so I would be reasonably confident of those dates. The "uncrossed legs" thing is something you'll often read when it comes to determining which coins were minted during Alexander's lifetime and which were minted afterwards. I'd ignore this rule entirely as it has so many exceptions as to be pretty useless on its own. Instead, the PELLA website I linked above is the best method for attributing and dating Alexander's coins - though it's not fullproof either and some stated dates are now known to be incorrect.
Hi, I am new to this forum and have recently purchased my first ancient coin from an auction. An Alexander III ‘the Great' lifetime Tetradrachm. Babylon mint. Head of Herakles right, wearing lion skin / Zeus Aëtophoros seated left; in left field, kylix above M, monogram below throne. Price 3652. Lightly toned, very minor doubling. EF.