problem GetUserFace

[nativecode2020]

Hi, I have a ZKTeco Iface 1000 and need to use the GetUserFace function, but it's returning null.

ICollection<UserTemplate> templates = new List<UserTemplate>(); string faceData = ""; int faceLength = 0;

for (int faceIndex = 0; faceIndex < 10; faceIndex++) { if (objCZKEM.GetUserFaceStr(machineNumber, enrollNumber, faceIndex, ref faceData, ref faceLength)) { templates.Add(new UserTemplate { TemplateIndex = faceIndex, TemplateData = faceData }); } }