Initiate Challenge

curl --request POST \
  --url https://api.authsignal.com/v1/challenge \
  --header 'Content-Type: application/json' \
  --data '{
  "verificationMethod": "SMS",
  "action": "signInWithSms",
  "phoneNumber": "+64271234567",
  "locale": "en"
}'

{
  "challengeId": "<string>",
  "expiresAt": 123
}