Recently we were calling InitializeForm function through WEB API, to which parameters to be passed were
TragetFieldType EnumType values:-
URL
https://xxx.crm.dynamics.com/api/data/v8.1/InitializeFrom(EntityMoniker=@p1,TargetEntityName=@p2,TargetFieldType=@p3)?@p1={‘@odata.id’:’accounts(AAA19CDD-88DF-E311-B8E5-6C3BE5A8B200)’}&@p2=’account’&@p3=Microsoft.Dynamics.CRM.TargetFieldType’All’
The Parameters
Please refer the below link to get a good understanding on Web API
https://debajmecrm.com/?s=web+api
Hope it helps..