In the beginning, I had also some confusing experiences until it finally worked. The packages
tmswebcorefnccorepkg.lpk
tmswebcorefncuipackpkg.lpk
are not supposed to compile at all. They are containing the informations how to replace the LCL versions of the FNC Core/FNC UI controls by their web versions during transpiling the fpc code by the pas2js transpiler. Unfortunately, when you include these packages into your project (you have to when using the FNC UI Pack) Lazarus tries to compile these packages, In both packages you have to change the package settings from
IDE Integration - Automatically rebuild as needed to Manual compilation (never automatically)
Furthermore you have to add the FNC Core and FNC UI Pack source pathes to your WebCore project. To be able to insert any FNC Core/FNC UI control onto your web form, you have to set
WebLib.;LCLTMSFNC
in Lazarus Tools - Options - Environment - TMS Web Core - Component Units
Finally it should all run smoothly. Another inconvinient thing is, that as soon you are adding more complex FNC UI controls on your web form, Lazarus is not adding all needed units. In case there are compiler (transpiler) error messages about missing or unknown classes, you have to add the needed units by yourself. Kind of clumsy.
Enjoy - Ulrich