How to use the bazinga64.Encoder.toBase64 function in bazinga64

private to_store(serialised: ArrayBuffer | string): string {
    return Encoder.toBase64(serialised).asString;
  }

private async sendExternalGenericMessage(
    sendingClientId: string,
    conversationId: string,
    asset: EncryptedAsset,
    preKeyBundles: UserPreKeyBundleMap
  ): Promise {
    const {cipherText, keyBytes, sha256} = asset;
    const messageId = ConversationService.createId();

    const externalMessage = this.protocolBuffers.External.create({
      otrKey: new Uint8Array(keyBytes),
      sha256: new Uint8Array(sha256),
    });

    const base64CipherText = Encoder.toBase64(cipherText).asString;

    const customTextMessage = this.protocolBuffers.GenericMessage.create({
      external: externalMessage,
      messageId,
    });

    const plainTextBuffer: Buffer = this.protocolBuffers.GenericMessage.encode(customTextMessage).finish();
    const recipients = await this.cryptographyService.encrypt(plainTextBuffer, preKeyBundles as UserPreKeyBundleMap);

    const message: NewOTRMessage = {
      data: base64CipherText,
      recipients,
      sender: sendingClientId,
    };

    return this.apiClient.conversation.api.postOTRMessage(sendingClientId, conversationId, message);

private to_store(serialised: ArrayBuffer | string): string {
    return Encoder.toBase64(serialised).asString;
  }
}

private async encryptPayloadForSession(
    sessionId: string,
    plainText: Uint8Array,
    base64EncodedPreKey: string,
  ): Promise {
    this.logger.log(`Encrypting Payload for session ID "${sessionId}"`);
    let encryptedPayload;

    try {
      const decodedPreKeyBundle: Uint8Array = Decoder.fromBase64(base64EncodedPreKey).asBytes;
      const payloadAsBuffer: ArrayBuffer = await this.cryptobox.encrypt(
        sessionId,
        plainText,
        decodedPreKeyBundle.buffer,
      );
      encryptedPayload = Encoder.toBase64(payloadAsBuffer).asString;
    } catch (error) {
      this.logger.error(`Could not encrypt payload: ${error.message}`);
      encryptedPayload = '💣';
    }

    return {sessionId, encryptedPayload};
  }