The error in the File Drop Automation is due to the filename pattern not matching exactly because of additional seconds and milliseconds in the filename. To resolve this issue:

Modify the Import File activity to use the %%FILENAME_FROM_TRIGGER%% personalization string. This ensures that the Import File activity dynamically accepts the filename exactly as it is uploaded to the SFTP location.

Update the filename pattern in the automation setup to avoid hardcoding the date format and instead rely on the filename that triggered the automation.

By using %%FILENAME_FROM_TRIGGER%%, the automation becomes flexible and will correctly handle any file name that matches the initial pattern triggering the automation, regardless of additional timestamp details.