Hello Sanjay
Can you check org structure in FI? Go to FS00 - take any GL account assigned to company code and tell me whether group account field has anyu value or not? Check the chart of account config too.
FSI is the standard entity type used to maintain group accounts of FI in MDG. If you COA has group COA then you have to create group COA first using FSI entity type then you can create account.
Kiran