At least one signature didn't pass verification

[Djihanegh]

Im getting this error

{"message":"At least one signature didn't pass verification"}

getting seed from mnemonic :
final seed = bip39.mnemonicToSeed(mnemonic);

getting SimpleKeyPair from seed :
final keyPair = await Ed25519().newKeyPairFromSeed(seed);

signing the transaction :
final signature = await Ed25519().sign( encodedTransaction, keyPair: keyPair );
any solution for this ?