curl --request POST \
  --url https://{instance}.omniapp.co/api/v1/users/email-only \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "email": "jsmith@example.com",
  "userAttributes": {}
}
'

{
  "email": "jsmith@example.com",
  "userId": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}