Does the melody of vocals have to go with instruments melody?

No, the melody of vocals does not have to go with the instruments melody. In fact, it can be quite interesting and complex when they are not in the same melody. This is because it creates a more dynamic and multi-dimensional sound. The vocals can provide a counterpoint to the instrumental melody, or they can even be in a completely different key. This can create a very unique and memorable sound that will keep listeners engaged.