Is it possible to pass a “custom evalscript” as base64 encoded parameter in a OGC WMS request within a leaflet webmap?

If yes, then please assist.

At the moment I have reference to this FAQ link that says this is possible, but I am struggling a little. I’m not quite sure how to structure the request for this to work.

Below is my attempt, but the response is 400.

const sentine2RGBLayer = L.tileLayer.wms(`${sentinelHubWMSBaseUrl}/${sentinel2InstanceID}`, {
        tileSize: 512,
        maxcc: 50,
        preset: "CUSTOM",
        datasource: "Sentinel-2 L1C",
        layers: "B01,B02,B03",
        evalscript: "cmV0dXJuIFtCMDgqMi41LEIwNCoyLjUsQjAzKjIuNV07",
        time: `2023-01-28`,
        transparent: "true",
        format: "image/png",
        crs: L.CRS.EPSG4326,
    });

Why do I need this? I would like to built custom script client side and then submit to Sentinel Hub as a WMS request.
I am specifically interested in rescaling and alternate color ramp changes to a layer (or custom script) for the visualization of data retrieved.
At the moment I succeed with calling configured layers, with preset color maps.

const sentine2RGBLayer = L.tileLayer.wms(`${sentinelHubWMSBaseUrl}/${sentinel2InstanceID}`, {
        tileSize: 512,
        maxcc: 50,
        layers: "TRUE-COLOR-S2-L1C",
        transparent: "true",
        format: "image/png",
        crs: L.CRS.EPSG4326,
    });

Thank you in advance.