Buy direct Ad space on websites

hi there, want start buying directly ad Spaces on websites ( blogs, forums etc. ) in specific niche. The thing that I don’t know how to deal with it is tool that will help me.

Like I contact publisher, we talk about cpm price, I send him creatives, but how booth of us can track impression? Like some shared dashboard where we booths see impressions.

Never doing direct media buy before, so will be happy for any tips.

Thank u