Wally: Pay only for messages that arrive

• Can I Message — Check whether a message to this person would be allowed, before trying to send it. Returns whether they have opted out, whether consent is on record, and whether the account has enough credit. Costs nothing and sends nothing. Use this whenever you are not certain a recipient is reachable.
• Send Message — Send one message to one person. Returns immediately with a queued status; delivery happens within about a minute. REFUSED if the recipient opted out, has no consent on record, or the account has insufficient credit. Never call this in a loop over a list of people without the account owner's explicit agreement, and tell them the total cost first.
• Get Message — Look up what happened to a message you sent: whether it was delivered, what it cost, and the carrier's reason if it failed.
• Search Contacts — Search the account's contacts by name, number or email. Shows whether each person can currently be messaged.
• Add Contact — Add somebody to the account's contacts. You must supply consent_note describing how this person actually agreed to be messaged; it is stored as evidence. Do not invent one. If the human has not told you how consent was obtained, ask them rather than guessing. Adding somebody who previously opted out does not resubscribe them.
• Get Account — The account's credit balance, message rates and whether it is approved for sending. Check this before doing anything that will send more than a handful of messages.

Schemas and invoke metadata: Directory API