Dear Hari,
There is customization which will impact while you trying to create a deal for purchase of bond.
Assign Flow Types to Update Types, Please check the customization which update type assigned for flow. Please find below customization path.
Treasury and Risk Management- Transaction Manager-Securities-Transaction Management-Update Types-Assign Flow Types to Update Types.
Update type start with DBT is for derived business transaction, there are mostly calculated for inflows. These are mostly premium or discounts for positions that are amortized.
Let me know if you need any more information.
Regards,
Jain