After trying multiple times, finally done it!)
Update 18/01/2022: their support reached out to me with a custom update for my problem. I sent them the log file and they got back in a day. The backup went ahead but then due to multiple WhatsApp backup attempts it stopped sending codes. Had to wait for 24 hours before installing the app on the target iphone and then after 3 failed attempts it finally restored my 22gb backup. Just one concern, I can see this data in the iOS section and not WhatsApp data in the storage information. I want control over this data and want it backed up on iCloud for whatsapp and not show in iOS storage forever. If you could help me show this data in WhatsApp section you get the 5 stars!! 15/01/2022: After trying multiple times for transferring the data it has not completed, keeps showing me the verification screen even after verifying. I have been blocked by WhatsApp for sending codes for 14 hours. Call/Chat support is not available. Waste of time & money.