Thank you for submitting your item for appraisal, this appears to be a silver tael / lạng ( equivalent to ten 10 tiền) of Thiệu Trị, third emperor of the Nguyễn Dynasty of Vietnam, 1840–1847 inscribed Thiệu Trị thông bảo , Vạn thế vĩnh lại 紹治通寳 萬世永賴 ( Thiệu Trị coin, ten thousand generations will have perpetual confidence) . Reverse 玦澒 千年化盪 鏐萬世傳 酬動彰有 德所寶者 誰賢 All coins I have come across have slight variations in the writing of characters. e.g. the "wan" 萬 character is also different from the coin you mentioned. I couldn´t find this particular variation in the literature. There is a small french contremarque in the rim of which I can not see any trace on the other side, which strikes me odd.
The estimate is based on similar offered or sold at auction.