Hello
I?m from Spain, new at this forum and love coins.
This coin (as say by Lonewolf) is part of an spanish coin but not an 8 reales, it could be a 4 reales (the 8 reales coin doesn?t have the assayer in that area).
The coin was struck at Lima in 1766 and the assayer was JM. It can be seem part of the last number 6 before the JM letters and the assayer JM signed between 1761 and 1773 (Charles III).
To be sure of the face value of the coin it must be weight. that coin should weight around 3,5 gr.
Saludos