Update a Sub-merchant

Send PUT /onboarding/v1/sub-merchants/{subMerchantId} with merchantId in the request header. The body uses the current update-sub-merchant DTO and supports the core identity, contact, company, tax, address, bank, status, citizenship, and compliance fields used by the create flow.

For document-based updates, use multipart PUT /onboarding/v1/sub-merchants/updateWithFile/{subMerchantId}. Country-specific document requirements apply. A successful response contains id and status.