If you share the OTP then hackers will get access to your account and all your personal messages and media. The hacker can then send messages to your friends/relatives and can also ask money from them.
What to do if this happens?
One should immediately reset WhatsApp and log in again. To avoid the scam, it's always advisable to not share any information without confirming if the message is genuine. Also, you may activate the two-factor authentication on WhatsApp to increase your account's security.
The new scam poses a serious threat as recently, WhatsApp received the nod for its UPI-based Payments facility from the National Payments Corporation of India (NPCI) which also uses OTPs for transactions. In view of this, if your WhatsApp account gets compromised, then not just the data, hackers are likely to get hold of your bank account details.
There have been incidents of frauds on other UPI apps as well in the past.