Maybe something went wrong?
If you go back and take a look at the code I left you a few posts above, you'll see that the R6 class (in your .b.r file) is called mannkendall (all lowercase) and not MannKendall like the function you want to use.
Then in the related .yaml file, name: it wants mannkendall and not MannKendall (as it appears in your files in the Github repository).
Intervene on the .yaml files or accept the PR.
The screenshot shows your form in action.
- mk_trend.png (153.03 KiB) Viewed 527 times
we're keen to get you underway!
Cheers,
Maurizio