In addition to the Redmine Outlook Add-In, we recommend installing the Redmine Shared API plugin.
It helps to adjust different API`s of Redmine and Outlook to each other.
Though Redmine Outlook Add-In works normally without the Redmine Shared API plugin, it may cause some issues connected with the server with such error messages:
Protocol Error. Please check your internet connection and try again.
The Redmine Shared API plugin also allows you to use Redmine Custom fields.
Using custom fields allows you to add specific hour start/end time slots to your Outlook calendar by using Start/End Time custom fields.
The Redmine Shared API plugin is developed by Ahau Software and is free for downloading and installation.
Contact your Redmine admin for the installation.