My Litecoin address is not valid

This is a very common error due to Litecoin changing it's P2SH's address format in 2017.

Litecoin addresses now start with "M" instead of "3" to avoid confusion with Bitcoin. Unfortunately, some sites don't support the new multisig addresses.

If you want to send Litecoin to a SegWit address, first you have to convert it to the legacy form using a converter. We recommend using https://litecoin-project.github.io/p2sh-convert/.

We also recommend you to use https://chainz.cryptoid.info/ltc/ instead of other Litecoin explorers as it supports the new addresses.