Creates a new Client Account (designee/customer) under your user.

Required

• client_type: individual or business
• first_name, last_name
• address_line_1, city, state, zip_code
• business_name — required when client_type is business

Optional

• country_code (defaults to US), address_line_2
• caf_number (9 digits, not all zeros), ptin (P + 8 digits)
• mobile_number, fax_number

On success you get a uuid. Use that ID in later tax transcript / CAF / ISP APIs. Creating an account also stores CAF/PTIN/fax history for that client.