NOWPayments checkout is not configured
Plan, traffic, or reseller top-up selected NOWPayments while it is not ready (balanceTopUp.nowPaymentsNotConfigured / 503).
Why this happens
Same family as Lemon Squeezy/Coinbase short “not configured” — credentials or enable flag incomplete.
Diagnose and fix
1. Enable NOWPayments checkout; fill API key (and IPN secret); save.
2. Retry premium/traffic/crypto purchase; member should get an invoice URL.
3. Offer another gateway if NOWPayments is not intentional.
4. Longer sibling includes the Admin path explicitly.