Not sure where the best place to post this. But here goes:
I never use this tool myself, but I frequently am cleaning up after others that do. Three problems that I have noticed:
(1) in the PMC parameter, the value should be a integer and not prefixed with "PMC":
|pmc=PMCxxxxxx (where xxxxx = integer)
The incorrect form throws an error that must be manually fixed.
(2) urls are sometimes added that are indentical to that already produced by
|pmc=. In this case, the url should be suppressed since it is redundant.
(3) Ref tags that take the form of ":0", ":1", ":2". While they are unique, they are not very informative. Better to create a Harvard style ref tag, the form of first authors last name + year of publication (i.e., "Smith_2017" is much more readable that ":0").