Also, note that the SegWit addresses used by default in Electrum are the bech32 addresses (aka "bc1").
Not all services/wallets are currently compatible with bech32 addresses. Exchanges (and gambling sites) seem to be the common services that won't recognise bech32 addresses and some block explorers don't work with them either.
If you need/want the backwards compatible "3-type" addresses (aka p2sh-segwit/"P2SH-P2WPKH"), you will need to follow the guide here:
https://bitcoinelectrum.com/creating-a-p2sh-segwit-wallet-with-electrum/ Make sure to take heed of the warning at the end of that guide. You might be better served generating a BIP39 seed mnemonic in a different wallet and then using that "proper" BIP39 seed mnemonic, rather than forcing an Electrum seed to be BIP39 and ignoring the "checksum failed" error.