this is the config file:
export const wallet = Keypair.fromSecretKey(Buffer.from('<YOUR_WALLET_SECRET_KEY>'))
This is the piece of code validating the secret key:

static fromSecretKey(secretKey, options) {
    if (secretKey.byteLength !== 64) {
      throw new Error('bad secret key size');
    }
    const publicKey = secretKey.slice(32, 64);
    if (!options || !options.skipValidation) {
      const privateScalar = secretKey.slice(0, 32);
      const computedPublicKey = getPublicKey(privateScalar);
      for (let ii = 0; ii < 32; ii++) {
        if (publicKey[ii] !== computedPublicKey[ii]) {
          throw new Error('provided secretKey is invalid');
        }
      }
    }
    return new Keypair({
      publicKey,
      secretKey
    });
  }

putting 88 character secret key throws and error, what am I doing wrong? what encoding should I use?

I found this advice:
Hello to use the Array Keys from solrwallet type of wallets
you have to use below code

const pk= [185,123,156,123,…,]. // Note this is without quotes.
const wallet = Keypair.fromSecretKey(Uint8Array.from(pk));

But I don’t understand it at all, since when does private key look like that?