HI dikshagoel,
Assuming this is for ACC
The internal name is something which is automatically generated for a new entity using the related Counter values which you can find inside Administration > Platform > Counters.
In your case when the child delivery is getting created it is taking an internal name for this there is another delivery exisiting inside the database table. Quite possible that the conflicting delivery was exported from another environment and imported in this instance.
it is there advised that you make use of a prefix string for entities by defining them in the Deployment Wizard.
Regards,
Vipul
