Hi Angel --
Hmmm. Better pictures are needed.
Consider the side with the shield. To the left of the shield is a large "S." This means the coin was minted in Seville, Spain. To the right of the shield is a small "o" with "iiii" under it. This means the denomination of the coin is 4 reales. The pictures do not give enough information to state anything else.
The coin may be genuine. We need to know which ruler the coin was minted under. His name appears on the outside to the right of the "iiii."
Look at the coin in my picture. You can make out "PHI" which are the first three letters of PHILIP, probably Philip II who reigned from 1556 to 1598. Can you make out any letters around the edge of the coin? I can't read any from your pictures.
Check this page:
It may help you figure out some letters. Write back if you figure anything out.
Your coin has been harshly cleaned, probably with silver polish. This means, even if genuine, your coin will be worth about 1/4 of its normal, uncleaned, value. The 4 reales in my picture sold for $460 US dollars during a 2021 auction.