A customer says checkout shows "No payment methods are currently available". Why?

That message appears when no payment method is switched on for that order. Check Settings → Store Settings → Payment Gateway:

• Is Cash on Delivery, Bank Transfer or UPI ticked in the Enabled column?
• Is any online gateway showing Live at checkout?
• If they shop in a different currency, does an enabled gateway list it under Supported Currency? Gateways are hidden for currencies they don't support.

If the shopper instead sees "Cash on Delivery isn't available for this order", that comes from Orders → Fraud Protection: High-risk orders is set to Block COD at checkout (force prepaid). Keep an online method enabled so those shoppers can still pay.