Why can't I activate Razorpay?

Check these on Settings → Store Settings → Payment Gateway:

1. The Online Payments plugin is active (if it is off, the page shows a link to turn it on).
2. Razorpay is ticked in the Payment Gateways box and you clicked Save gateways. If it won't tick, you have used all the gateways your plan allows — untick another or buy more Gateway Capacity.
3. Click Configure, enter your Key ID and Key Secret for the mode you chose (Live or Sandbox) and the Webhook Secret, set Status to Active and click Submit.

Razorpay must also have approved your account; until then, take orders with COD and UPI.