curl --request POST \
  --url https://api.withampersand.com/v1/billingAccounts/{billingAccountId}/portalSession \
  --header 'Content-Type: application/json' \
  --header 'X-Api-Key: <api-key>' \
  --data '{
  "redirectUrl": "https://dashboard.withampersand.com/the-current-page",
  "timeout": 3600
}'

{
  "url": "https://billing.portal.com/customer/session"
}