SOLUTION:

If you want to have SAME number for Business Partner Number and Customer/Vendor Master Number.

1. Ensure both BP Grouping Number range Interval and Customer/Vendor Number Range Interval are similar.

2. Ensure Customer/Vendor Account Group number range interval have External ticked.

STEP 1: Go to Transaction code BUCF, Ensure BP Grouping Number range Interval in similar to Customer Account Group Number range Interval

STEP 2: Go to Transaction code XDN1, ensure the Number Range Interval have External Ticked

Thanks,

Adharsh K S