Check first you are typing the correct phone number:
1. A 10 numbers mobile phone number
2. Without input +91 country code
3. Can't input a local phone number
＊Correct example: 9876543210

If you checked you are typing the correct phone number, but you still can't register:

1. OTP system maybe too busy, try again 5 mins later
2. OTP mail maybe blocked by your phone, check your junk mail box and setting
3. OTP mail maybe blocked by your telecom, contact your phone service provider
4. Your network maybe disabled or not stable, try to move to an open space with  fine network signal and re-open network connection again
5. This phone number maybe has registered already, try to use login again
6. When you are using a second-hand phone number, this phone number maybe has registered already, try to use a new phone number instead
7. When you are using a second-hand phone, this phone maybe installed already, try to delete and clean app data, then install again.