curl --request POST \
  --url https://external.dev.onboardpay.co/auth/user-auth/initiate \
  --header 'Content-Type: application/json' \
  --header 'x-signature: <api-key>' \
  --data '{
  "email": "<string>"
}'

{
  "authSessionId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "isReturning": false
}