Create a product attribute set. Product attributes and sets have entity type id as 4. Skeleton id is the id of the attribute set used as a base.
Sample Curl
curl --location 'https://mygatewayurl.com/V1/admin/product/attribute-set/' --header 'Content-Type: application/json' --header 'Authorization: Bearer arn54g3xo6vsw4kl5gu2m233qirtfrru' --data '{"attributeSet":{"attribute_set_name":"Glyde test via API","sort_order":0,"entity_type_id":4},"skeletonId":4}'