I am trying to get standard and custom attributes of an entity. I am using following API 
GET [Organization URI]/api/data/v9.0/EntityDefinitions(LogicalName='contact')/Attributes?$select=LogicalName,AttributeType,SchemaName,IsCustomAttribute,IsValidODataAttribute,EntityLogicalName&$filter=IsValidODataAttribute eq true and IsValidForRead eq true
Though it return all the attributes but when I try to get these attributes data by using following API
GET [Organization URI]/api/data/v9.0/contacts?$select=emailaddress3,slaid,emailaddress2,emailaddress1,.....
The API return response: "Could not find a property named 'slaid' on type 'Microsoft.Dynamics.CRM.contact'."
I get this message for following properties:
createdbyexternalparty, slaid, parentcontactid, slainvokedid, modifiedbyexternalparty, accountid, parentcustomerid
by removing these fields from select filter, API returns 200 response.
Is there is anything I am missing or need to add some filter while getting attributes information?
Thank you!