Is the zakat that was previously paid—due to ignorance of the money not reaching the nisab—considered accepted, or sadaqah, or not accepted at all?

Zakat is obligatory on gold, silver, and money under two conditions: reaching the nisab (minimum threshold) and the passing of one lunar year (hawl). The nisab for gold is 85 grams, and for silver, it is 595 grams. Zakat becomes obligatory on money if it reaches the nisab of either gold or silver. If the wealth is below the nisab, Zakat is not obligatory, but its owner may voluntarily give charity, and they will be rewarded for it. This is affirmed by the letter of Abu Bakr (may Allah be pleased with him) regarding Zakat, in which it states: "Whoever has only four camels, there is no charity due on them unless their owner wills it," and "On silver, one-quarter of a tenth is due. If one has only one hundred and ninety [dirhams], there is nothing due on it unless its owner wills it," meaning unless they voluntarily give. Therefore, giving Zakat without reaching the nisab is considered an act of charity and voluntary giving.