Probably SI5351 library needs to be 1.1.2 (manage library, filter on SI5351 and select previous version and install. V2 is beta and uses different parameters for several functions).
I downloaded the repository and installed the Si5351 library.? I discovered that the sketch does not compile with the latest version of the Si5351 library, version 2.?
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I've just submitted a pull request on GitHub which adds instructions to the README which describe the installation process for version 1.1.1 of the Si5351 library.