"at the spot" mean "at the scene/place of an event" "on the spot"-it's an idiom-mean "right now/at once/without delay" (p/s:Hi,i'm not a guy^-^...hope it help:)

Meeting on the spot has an unusual meaning, because it is an idiom. This means the meaning does not match the words. Meeting on the spot means meat quickly - immediately. The normal words for this is: "I will be there on the spot." = I will be there right away. Meet me at the spot, is something you would say if you were talking to a person and did not want to say where you will meet(because you do not want anyone to overhear) - but that place is already known by you both, and you have probably met there multiple times in the past. The "Spot" is not used often in normal speech unless one of these situations is happening. If you wanted to say to someone that you will meet them somewhere (and being over heard is not an issue you wanted to elude too), you would say something like, "I will see you there."