How to make the advertising sponsor work for the listing?

Hi all Im new to selling on amazon, tried to do a campaign manager for the listing, it shows as active but it says ineligible ? I am the only person who has this product so was a bit confused. and from what i understand you have to wait 90 days before you can have an offer on the buy box, correct? not a sale as of yet, any help or advice would be much appreciated

thank you in advance

Yes, you have to qualify for the buy box - which timewise is 90 plus days.
You can do other advertising yourself, just not the sponsored ads part yet.