Have anyone sort this out? The last version was a nested API controller from Umbraco 8 this is for Umbraco 9+. var nestedContents = currentEventPage.Value<IEnumerable>("registeredParticipantsNew", umbracoEvent.CultureName); "UmbracoParticipant" is a custom model for the Block list items. I want to populate a new participant to the Block list and then send it back with SetValue to the specific node in Umbraco.

Back in the day, you had to do it like the code at the bottom of this page: https://github.com/umbraco/UmbracoDocs/blob/e64ec0e5b28b4e5a37b7865691621e45dd82701f/Getting-Started/Backoffice/Property-Editors/Built-in-Property-Editors/Block-List-Editor/index.md but not sure if that's still the case.

Thanks, seems like this is the way to do it even for Umbraco 13. But feels like a hard way of solving this kind of data handling.

I've been doing this recently and this is how I've done it. It gets even more complex when you have a blocklist within a blocklist. I ended up cheating (for a one-off import) by grabbing the existing json from a test page and inserting the relevant part with string interpolation. I've a todo item to go back and do it properly as an exercise if I ever have the time.