The phones should be either connected to the same Wi-Fi, or the Android one must be connected to the iPhone's hotspot. Android phone should run WhatsApp version 2.22.7.74.
How to perform the transfer
Install 'Move to iOS' app on Android. Enter the code that appears on your iPhone when prompted. Click 'Continue' and then select WhatsApp on the 'Transfer Data' screen.
Use same phone number
Once the data transfer is complete, install WhatsApp on your iPhone. Now, login to the app using the same phone number. Tap 'Start' when prompted and let the process complete.
Call history will not be transferred
WhatsApp data transfer from Android to iPhone will not let you move peer-to-peer payment messages or call history. iCloud backup will have to be done manually.