Rodrigo S. okay - so are you trying to import a new site to webflow with a clean style guide? Or are you trying to import just a section or page, to an existing site?
If just a section, I would just hit copy in site builder then go to webflow and hit paste - i would bother with the Webflow app personally but I understand why you might go with the webflow app because its right inside of Webflow but I do think there may be some outlier issues with that right now since the most common use case right now is a clean style guide and importing your pages, then customizing the style guide and going from there. We have several bugs that have been filed but do not have ETAs.