大家好！应用程序提交审请时有个问题请教 （非消耗型产品）提示 购卖商品 ID不存在 应该如何解决

Trying to enable TTP and we're a PSP, from everything I'm reading I'm supposed to provide a reader token to our merchants but can't find anything on it. How do I generate this token? All I know is that it's a jwt and there's some header requirements. Documentation mentions the jwt should include a unique merchant identifier. My question is what does the payload and header look like when signing the jwt?