API returns status code 500 with error code 4000

Hello. We need some help.

Sometimes we have API returns status code 500 with error code 4000. Example of error body:

{

 statusCode: 500,

 errorCode: 4000,

 message: 'An unexpected error has occurred. 

 Please contact the Support team at https://help.smartsheet.com/contact for assis tance.',

 refId: '1epuw7ruti51a'

}

This happens in random requests to random routes.

For example, simple request which returns this error now:

To sendRows:

{

  body: {

    sendTo: [{ email: 'dmft@yandex.ru' }],

    subject: 'Подтверждённая съёмка: ...',

    includeAttachments: true,

    includeDiscussions: true,

    rowIds: [1843734197495684]

  },

  sheetId: 7250500555958148

}

We make many requests like above. But this one is not respond correctly.