2853942 - Error R1092: Migration of Customer

While performing the migration for Customer with internal number range assignment below error occurs;

Grouping xxxx has internal number assignment, do not enter a number
Message no. R1092

Leaving the field empty the following error occurs:

Tab S_CUST_GEN, field Customer Number, line X is empty; enter value for the mandatory field

• S/4HANA Cloud
• S/4HANA On-Prem
• Migration Cockpit 

R1092, R1 092, Gruppierung & hat interne Nummernvergabe; geben Sie keine Nummer ein , KBA , CA-GTF-MIG , SAP S/4HANA Data Migration Cockpit Content (LTMC) , LO-MD-BP , Business Partners , How To