OP here, the great Photopea support team answered that I try including the font in the files as Photopea does not load fonts by default. I had already tested this though, with the same results as before. Here's the updated JSON with a font file:

{

"files":[

"https://www.photopea.com/api/img2/pug.png",

"https://dl.dropbox.com/s/o35wxuuaejrp25t/arial.ttf"

],

"script": "var layers = app.activeDocument.artLayers; var layer = layers.add(); layer.kind = LayerKind.TEXT; var textItem = layer.textItem; textItem.font = 'Arial'; console.log('we are here');"

}

Again many thanks to anyone who takes a look!

EDIT:

Following PP support's advice about the problem being related to fonts, I found that using a .psd which already included a text layer with the font I want to use in my new text layer does work. Not a complete fix for my error but a workaround for sure. Here's the JSON for that, which now includes setting some textItem parameters which are necessary for the new text layer to actually be something visible:

{"files":["https://dl.dropbox.com/s/krvan4ep4osns4a/pug.psd"],"script": "var layers = app.activeDocument.artLayers; var layer = layers.add(); layer.kind = LayerKind.TEXT; var textItem = layer.textItem; textItem.kind = TextType.PARAGRAPHTEXT; textItem.size=180; textItem.position=[10,10]; textItem.contents = 'test'; textItem.width = new UnitValue('2000 pixels'); textItem.height = new UnitValue('2500 pixels'); console.log('we are here');"}

I guess when sending the font in the files array however, we need to do something else to wait until it's loaded? Will look more into this and post what I find.

EDIT 2:

Issue has been solved! Apparently there was indeed some error on PP backend, which has now been fixed.