Attempt to change column values, get an error about pulse subscription

With the following command:

mutation request($boardId:Int! $itemId:Int $columnValues:JSON! $createLabelsIfMissing:Boolean!) { change_multiple_column_values (board_id: $boardId, item_id: $itemId, column_values: $columnValues, create_labels_if_missing: $createLabelsIfMissing) { id }}

-and valid values-

I got the following response:

{“error_code”:“RecordInvalidException”,“status_code”:422,“error_message”:“Validation failed: user cant subscribe to a pulse without being exposed to it”,“error_data”:{“error_data”:“Validation failed: user cant subscribe to a pulse without being exposed to it”}}

In other words, a message about subscribing to a pulse, while the request was to change multiple column values. How do I deal with such error messages?
I recorded the response headers, here is a selection:

I tried the same request a few minutes later and go no error anymore. But why was this error returned the first time?

Thank for your insights!