Partially updates a Client Account you own. Send only the fields you want to change; the body must not be empty and must include at least one updatable field.

Typical uses: fix address, add or correct CAF/PTIN, or change contact info before CAF/ISP steps that require a complete client.

If you change country_code, include a valid state and zip_code for that country. Same field rules as create (e.g. CAF = 9 digits, PTIN = P + 8 digits). Business accounts still need business_name when type is business.