Short answer — for domestic (Sri Lanka) mobile transactions, the lowest-fee apps depend on the transaction type:

• P2P (wallet-to-wallet / send-by-mobile): most wallets/apps offer free in‑wallet P2P. Examples: mCash (mCash→mCash free), Sampath WePay (wallet→wallet free) and FriMi (send by mobile number free). (mobitel.lk, sampath.lk, frimi.lk)

• Inter‑bank fund transfers (sending to another bank account): among popular apps the lowest advertised flat fees I found are around Rs.25–30 per transfer — FriMi shows Rs.25 per interbank transfer (one of the cheapest published rates), while Sampath WePay and several bank apps show ~Rs.30. If you transfer inside the same bank it’s commonly free. (frimi.lk, sampath.lk)

• Merchant QR payments (LANKAQR): many LankaQR‑enabled bank apps charge no fee to the payer; merchant MDRs vary and some banks have special promotions (HNB announced 0% MDR for LANKAQR merchants for certain transactions under Rs.10,000 in 2025). LankaPay’s LankaQR scheme aims for low charges (max ~1% is referenced for some providers). (lankapay.net, hnb.net)

What I recommend (practical):

• If you only move money between users of the same wallet/app, use that wallet (mCash, FriMi, WePay) — P2P is commonly free. (mobitel.lk, frimi.lk)
• For sending to other banks, check FriMi first (Rs.25 listed) and compare with your own bank’s mobile app — many banks charge ~Rs.25–30 per interbank transfer. (frimi.lk, sampath.lk)
• For merchant payments, scan LankaQR with any LankaQR‑enabled app; look for ongoing MDR promotions from specific banks (e.g., HNB’s 0% MDR campaign in 2025). (lankapay.net, hnb.net)

Caveats

• Fees change frequently and some offers are promotional. The statements above are based on the banks/wallet pages and press releases I checked (current as of Sept 7, 2025). Always verify the latest tariff page or in‑app fee schedule before making large or frequent transfers. (frimi.lk, sampath.lk, boc.lk)

If you want, I can:

• Compare the current fee tables for the specific two or three banks/apps you use (I’ll pull the latest fee pages and show a side‑by‑side), or
• Check international remittance apps (Wise, Remitly, etc.) if you meant cross‑border transfers.