There are some libraries you could use to utilize a pre-made API, but if you prefer to do it from scratch, like I did, you can take a look at this here: https://github.com/BlockHorizons/Bl...ting/src/BlockHorizons/BlockSniper/ui/windows It has the arrays for multiple windows, so examples enough. If you json_encode the arrays in those files as an example and put them in the ModalFormRequestPacket->formData, you should be fine.