Yes, you can, but: If a user clicks on your ad in Campaign 1, but doesn’t convert, they might click on an ad in Campaign 2 at a later point and convert. If that happens, Facebook will count two conversions: One in Campaign 1, one in Campaign 2. …
https://www.quora.com/Can-you-use-the-same-Facebook-Conversion-pixel-on-multiple-landing-pages