Any application using the Metadata object on Box's API.
Steps To Resolve
If applying metadata to a file/folder, use the templateKey of the metadata schema in the body of the request. If updating metadata to a file/folder, check that you have applied metadata to the file/folder first.
This error is caused when the metadata template is not found, either because the display name was used instead of the templateKey, or because the application is attempting to update metadata when no metadata schema exists on the file/folder yet.