One question: if my UTM coordinates in 3 zone width (0.9999 scale). How to reduce to this one?

The zone width is defined to 6°, cf. UTM zone definition. If you have a special (local) projection, you have to reduce the distances by your own, defined by your special crs.

Please note, all projections are applied only to horizontal distances (but not to slope distances!).

/Micha

In your programing, I see you use the reduction in 6 zone width (0.9996 scale).

Thank you very much.
Nguyen

When I set up 100 meters for horizontal reduction , my project does not work.

I take a look to your provided coordinate files. Here, the UTM zone number is missing and, thus, the simple check of your coordinates failed, i.e.,

if (yS >= 1100000 && yS <= 59800000 && yE >= 1100000 && yE <= 59800000) {
  // do reduction
}

kind regards
Micha

When I set up 100 meters for horizontal reduction , my project does not work.
This is my project link

https://drive.google.com/drive/folders/1Y5kRB5XILqdxwL-SJ8w41k3Kcfmv5EVP?usp=sharing
Thank you very much.
Nguyen