Create a source that can be attached to a CONTEXT_SOURCE_LIST attribute on a Product (for example the universal Images attribute).

Submit as multipart/form-data. The type form field discriminates the payload carried on value: for FILE, send the file bytes as the value multipart part; for TEXT, URL, and KNOWLEDGE, send the payload as the value form field.

Take the id from the response and include it in the attribute value on a subsequent POST /v1/products or PATCH /v1/products/{productId} call. Attributes currently accept FILE sources only, and may narrow that further — the Images attribute takes PNG and JPEG — so a source created here is rejected at attach time if it does not qualify.