Cannot insert duplicate key row in object with unique index . The duplicate key value

I am new to Outsystems and SQL. I am try to create a Bus Application where the entities are

When I try to create a new rider with the same name and different Route and bus Id. I get
Cannot insert duplicate key row in object 'dbo.OSUSR_6SL_RIDER' with unique index 'OSIDX_OSUSR_6SL_RIDER_4NAME'. The duplicate key value is (ABC). The statement has been terminated.
When I check Name field in the database table 'dbo.OSUSR_6SL_RIDER' it is not having the unique identifier set up. Can anybody please help me with this.