For a long time, Airtel allowed only limited denominations (like Rs 50, 100, 200) to be recharged online for prepaid users. This was done ostensibly to minimize errors on airtel recharge. However, it meant a lot of Airtel users preferred to recharge offline , specially for airtel rate cutters, airtel message packs and airtel data plans (GPRS packs, 3G packs) and so on. This restriction has today been removed and we have already made it live on mobikwik.com
So, if you are an Airtel user, feel free to enter any amount between 10 and 10000 at Mobikwik and your recharge should go through!
If you face any problem, feel free to file a support ticket at Mobikwik Support