Retrieve the customer by id

curl --request POST \
  --url https://api.sand.getivy.de/api/service/customer/retrieve \
  --header 'Content-Type: application/json' \
  --header 'X-Ivy-Api-Key: <api-key>' \
  --data '{
  "id": "<string>"
}'

{
  "id": "<string>",
  "emailAddress": "<string>",
  "merchantId": "<string>"
}