Method: identify the exact context your input lands in, then craft the payload that breaks OUT of that context. Prove execution by making your injected JavaScript call /m03/api/solve/r_href (e.g. with fetch()). No external collector needed. Server-rendered sinks also auto-mark once a value that would run is reflected/stored here.
The value becomes the destination of a link. Angle-bracket payloads are pointless - the interesting question is what URL schemes the app forgot to reject before putting your value into href.