Account group in ERP and its mapping relationship with CRM partner group

I have created one Sales customer via tcode VD01 in ERP:

And I have defined a request in tcode R3AR2 to try to download it to CRM via request download:

After download is finished, I saw following error message in tcode SMW01:

Error message: Number not in interval XXX - XXX

Why middleware complains this very interval 0000300000 - 0000399999? Where does it come from?

When the customer is downloaded into ERP from CRM, the business partner will be created with a proper number. The number range is maintained based on mapped CRM partner group, in this example 0002:

Here you assign the number range setting to the mapped group 0002.

In my system, currently group 0002 is assigned with number range 07:

This explains why 0000300000 ~ 0000399999 is complained in error message.

After I reassign group 0002 with correct number range 03, the issue is resolved.

By the way, I learned the knowledge above by debugging this function module below: