Send a physical letter via USPS — print and mail automatically
recipientrequiredcontentrequiredpaper_sizeoptionalcoloroptionalclawcard agent pay mail-letter '{"recipient": {"name": "John Doe", "address": "123 Main St", "city": "New York", "state": "NY", "zip": "10001"}, "content": "Dear John..."}' --jsonPOST https://www.clawcard.sh/api/catalog/mail-letterRequires API key in Authorization header. Balance deducted per call.