Difference between PM-Kisan eKYC by OTP, biometric and face authentication, which one should I use?

All three reach the same goal of verifying that you are the real Aadhaar holder, but they suit different situations. OTP based eKYC is done on the PM-Kisan portal by entering your Aadhaar number and the one time password sent to the mobile number that is registered with your Aadhaar. This is the easiest and free, but it only works if your mobile number is linked to Aadhaar. In your case, since your mobile is not linked to Aadhaar, OTP eKYC will fail because the OTP will go to whatever old number is in the Aadhaar database. Biometric eKYC is done at a CSC or Common Service Centre where the operator scans your fingerprint on a device. This works even if no mobile is linked, because your fingerprint is the proof. There is usually a small CSC service charge. Face authentication eKYC is done through the official PM-Kisan mobile app, where you scan your own face using the phone camera and the Aadhaar Face RD app. This is useful for old farmers whose fingerprints do not scan well and who do not have a linked mobile. For you, the practical choice is either get your mobile number updated in Aadhaar at an Aadhaar centre and then do OTP at home, or simply go to a CSC for biometric eKYC, or try the face authentication on the app. Always do this only on the official pmkisan.gov.in portal or the official app, never on a random link.