Dynamics 365 v9.x- How to add Lookup and Option Set in Alternate Key

Steps

Create/select existing a fields for required entity.
Add fields in Alternate Key
Upsert using code

Steps in Detailed

We will consider Lookup,Optionset and string data type fields for alternate key.

2. Create a new Alternate Key

3. Upsert using Code

For lookup, parse GUID to string format.
For Optionset, parse int value to string format.

Code snapshot

KeyAttributeCollection KeyAttributeCollection = new KeyAttributeCollection();                 KeyAttributeCollection.Add("apsm_fieldmapping_fieldid", fieldMappingId.ToString());                 KeyAttributeCollection.Add("apsm_slot_value", optionsetValueCount.ToString());                 KeyAttributeCollection.Add("apsm_os_type", "896950000");                 Entity entity = new Entity("account");                 entity.KeyAttributes = KeyAttributeCollection;                 entity["name"] = "Test Account for Alternate Key";                 UpsertRequest req = new UpsertRequest()                 {                     Target = entity                 };                 UpsertResponse upsertResponse = (UpsertResponse)service.Execute(req);