Lent money and only have WhatsApp chats as proof

What usually matters in this situation, and the papers to keep ready before you meet an advocate or free legal aid (call 15100).

Your situation

Is there anything in writing showing it was a loan? Messages where they accept they owe me

A dated list of every amount given and every amount repaid
Your advocate needs the exact balance claimed. Where: Your statements and notes.
Ask your advocate whether to send a written demand or a legal notice
A demand and the reply (or silence) can matter later. Where: —

Complete chat where they accept the debt or promise to repay
Shows the money was a loan and may affect time limits. Where: WhatsApp, SMS, email.
Borrower's full name and current address
Needed for a notice or a case. Where: Your records.

Transfer records (statement, UPI history, cheque encashment) — Proves payment and the date.
Proof of where the cash came from (withdrawal slip or statement) and when it was handed over — Supports a cash loan.
Records of any part-payments they made — Part-payment supports the loan and may affect time limits.
The original cheque and the bank's return memo — Needed for a cheque-bounce case.
The cheque (check its date) — Cheques are generally valid for 3 months from their date.
Names and contact details of people present — Can support an oral loan.
Your written demand and any reply — Their response may admit or dispute the debt.

Time limits apply to money claims. A written acknowledgement or part-payment can affect them. Your advocate will check.

General information, not legal advice.