ERC721PresetMinterPauserAutoId tokenURL error

I am working on writing ERC721 smart contracts by using the PresetMinterPauserAutoId script.

ERC721PresetMinterPauserAutoId("Simple", "SPL", "")  

However, for the third parameter in the constructor (supposing it's the base url), I am not sure what to put. I tried "ipfs://{CID}" , "http://ipfs/{local site}/{CID}" and "{CID}" but they all failed. I wonder how am I supposed tyo get my json data read and if there's any way to test what the input actualy is (in order to debug). Thanks.

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