The config_form.yaml and config_list.yaml for the galleries controller are using an incorrect syntax to refer to the path to the fields.yaml and columns.yaml files for the current stable release of OctoberCMS.

To fix this issue until the author updates the plugin, modify the config_form.yaml and config_list.yaml configuration files found in /plugins/raviraj/rjgallery/controllers/galleries/

The current values are:

config_form.yaml: @/plugins/raviraj/rjgallery/models/gallery/fields.yaml
config_list.yaml: @/plugins/raviraj/rjgallery/models/gallery/columns.yaml

The correct values are:

config_form.yaml: $/raviraj/rjgallery/models/gallery/fields.yaml
config_list.yaml: $/raviraj/rjgallery/models/gallery/columns.yaml