auto generation order/serial number

Hello everyone,*

i'm writing to you because i'm a bit stuck.*

I'm a beginner user of Excel VBA..

I'm trying to create a Userform where I can add new entry for my database.*
The userform is working but i'd like to add a Line code to generate automatically a Serial/Order Number.*

I have already found some solutions, I tried to do it on my own but it doesn't work on my UserForm.
Anyone can check my File and tell me where is the problem?

Problem : I want to generate a order/serial number each time I enter a new entry, but the serial/order number stay "0001"

I attached the file in this Post