Getting: 'exp' claim. Should be an integer [400 Bad Request] invalid_grant

function readFiles(folderId, client, queryData, countryCode, retryFlag) {
  return new Promise((resolve, reject) => {
    try {
      var dir = normalPath.normalize(path.join(__dirname, "/../fileStorage"));
      var allowIZ = /(\.i6z)$/i;
      fs.readdir(dir, (err, file) => {
        file.forEach(async function (filePath) {
          try {
            console.log(filePath);
            if (allowIZ.exec(filePath)) {
              var stream = fs.createReadStream(normalPath.normalize(path.join(dir, "/" + filePath)));
              let file = await client.files.uploadFile(folderId, filePath, stream)
              let updatedFile = await client.files.update(file.entries[0].id, { shared_link: {} })
              let url = updatedFile.shared_link.download_url;
              resolve(uploadID(updatedFile.id, filePath, queryData.id, url, countryCode));
            }//if
          } catch (e) {
            if (!retryFlag) {
              let retryResponse = await this.readFiles(folderId, client, queryData, countryCode, true);
              resolve(retryResponse);
            } else {
              if (e.statusCode == 500) {
                resolve('500')
              } else if (e.statusCode == 400 || e.statusCode == 409) {
                resolve('400')
              } else if (e instanceof ReferenceError) {
                resolve('refError');
              } else if (e instanceof TypeError) {
                resolve('typeError');
              }
            }
            reject(e)
          }
        });//forEach
      });//readDir
    } catch (e) {
      if (e.statusCode == 500) {
        resolve(0)
      } else if (e.statusCode == 400) {
        resolve(1)
      }
      reject(e)
    }
  });
}