Litecoin has several address formats: L… (legacy), M… and the older 3… (P2SH), ltc1… (native SegWit) and ltcmweb1… (MWEB). A service rejecting your address usually means it does not support that particular format.
Why 3 and M both exist
Litecoin P2SH addresses first shared Bitcoin's version byte and started with 3. A separate prefix (addresses starting with M) was added later; Litecoin Core's chain parameters list both. The same script can be shown as 3… or M…, but many services now accept only the new form.
MWEB addresses
MWEB, described in LIP-0003, needs a sender that can build MWEB transactions, so most exchanges reject ltcmweb1. More in our Litecoin fees and MWEB guide.
Keep an ltc1 address as your default for deposits and swaps.
Never copy addresses from old chats.
What to use for a swap
For a payout on the USDT to LTC page, generate a fresh ltc1…, L… or M… address in your wallet. Do not send LTC to a 3… address unless you are sure a Litecoin wallet issued it: a Bitcoin 3-address would receive the coins on the Litecoin chain under the same script hash, and only someone who can sign that script on Litecoin could move them.
Avoid random online 3-to-M converters as well. A conversion bug sends coins to an address nobody controls; generating a new address in your own wallet is simpler and safer. Before pasting, run it through the address validator, which shows the network and type.
FAQ
Are Litecoin 3 and M addresses different wallets?
Not necessarily; they can encode the same script hash with different prefixes.
Why is my ltcmweb1 address rejected?
Most services cannot send MWEB transactions. Use a regular ltc1 or L address.