
The Web Api method “RetrieveAllEntities” function can be a bit confusing as it was not included in the early versions and will give you errors, if you have the older end point hardcoded in your code.
GET {{webapiurl}}RetrieveAllEntities(EntityFilters=Microsoft.Dynamics.CRM.EntityFilters'Entity', RetrieveAsIfPublished=true)
This function should be used with caution and appropriate filters, since it can return a huge amount of data. Read mode about the function here