Here the 1858 Wright edition accidentally replaced the plural lyings with the singular lying. The correct plural reading was restored to the RLDS text in 1908. The critical text will follow the earliest reading, with its plural lyings. For a complete discussion of cases showing variation between lying and lyings in the text, see under Alma 12:1, 3.
Summary: Maintain in 3 Nephi 1:29 the plural lyings, the reading of both 𝓟 and the 1830 edition (“by their lyings and their flattering words”).