NOWPayments did not return an invoice URL
API key was present and the create-invoice call returned a body without an invoice URL (nowpayments-api).
Why this happens
Unexpected API response, account restriction, currency/pair not allowed, or NOWPayments outage. Not the “API key missing” path.
Diagnose and fix
1. Check NOWPayments dashboard status and allowed currencies for the API key.
2. Review app logs for the raw error/response.
3. Confirm API key environment (sandbox vs live) matches settings.
4. Fall back to another gateway if NOWPayments stays broken.