Why this plant is going down

How to solve this

Avoid excess water, bore a hole at base of the pot. It seems lack of air to the roots. If still it shows wilting symptoms, then there would be fungal infection

I bought a bundle yesterday stem and leaves are very soft and clean but leggy roots are good

Yes, it seems good some times, but roots also need aeration, which is available naturally in field. In potted plants it may not be

Examine after boring hole at base of pot

agree with alfonso sir