Issue
An error of "Validation Errors While Saving Record(s) There were custom validation error(s) encountered while saving the affected record(s). The first validation error encountered was "Record Type ID: value not valid for the entity: DDP"." occurs when trying to create a new Document Package in Salesforce Classic in an environment that has a fresh install of Drawloop.
Resolution
Setup > Profiles -> [Profile of user creating Document Package] -> Object Settings -> DocGen Package: Edit -> set "Opportunity" as the Default Record Type
Alternate solution for updating Default Record Type
Setup > Profiles -> [Profile of user creating Document Package]: scroll to "Custom Record Type Settings" -> DocGen Packages: Edit -> set "Opportunity" as the Default Record Type