I'm doing a translation about an invoice process from spanish to english and not quite sure how to translate "timbre" (in spanish) to english not sure if would it stamp/stamp number/seal
Any help would it be appreciated.
As I suspected, the reference is to a specific legal process that just does not apply in other countries or apply in the same way. I also notice that the website you referred to does not even try to translate timbre fiscal despite otherwise being in very good English.
Depending on how many times the words occur in the document you are translating, you have two main options: if they occur many times don't translate the term at all but just explain it once at the first occurrence - 'timbre fiscal' (official stamp of the tax authorities); alternatively if the words occur just once or twice translate as 'official stamp'.