If you use top-load liquid in a front-load machine: The top-load liquid creates too much foam. In a front-load machine, this foam can overflow and cause a ‘Suds Lock’. Your clothes will have soap stains, and the foam-water mix can enter the machine’s pump and circuit boards, causing it to break down quickly.
If you use front-load liquid in a top-load machine: Nothing dangerous will happen, but because there’s more water in a top-load machine, the front-load liquid won’t create enough foam. This means your clothes won’t get properly clean, and you’ll waste a lot of detergent.
The final word: Always follow the washing machine maker’s instructions. Choosing the right detergent will not only clean your clothes better but also increase your machine’s lifespan.