The publisher wants the APA-style for citations in my publication. Previously, I used the natbib package with the dinat style. When I change the package to apacite with the option natbibapa and the style to apacite, I get the following error:

File ended while scanning use of UL@on. bibliography{literatur}

Minimal working example

root file

input{res/praeambel}

begin{document}

onehalfspacing

   section{Section}
      Some example text citep{klafki2007:neueStudien}. 

      Another one: citeyear{kmk2004:bildungsstandardsPhysikAHR}

      Citing some articles cite{sadlerEtAl2007:SSI}

   addcontentsline{toc}{section}{Literatur}
   bibliography{literatur}
  
end{document}

preaeambel

documentclass[12pt]{scrartcl}

usepackage{ucs}                
usepackage[utf8x]{inputenc}
usepackage[T1]{fontenc}

usepackage[ngerman]{babel}

usepackage{graphicx}
usepackage{caption}
usepackage{subcaption}
usepackage{enumitem}

renewcommand{labelenumi}{theenumi)}

usepackage{amsmath,amssymb,amstext,amsthm}

usepackage{natbib}
bibliographystyle{dinat}

usepackage{setspace}

usepackage{ulem}

usepackage{geometry}
geometry{a4paper, top=20mm, left=25mm, right=25mm, bottom=20mm,
headsep=5mm, footskip=10mm}

usepackage{booktabs}

usepackage{ebgaramond}
usepackage{AlegreyaSans}

usepackage{hyperref}
hypersetup{hidelinks}

literatur.bib

@Article{sadlerEtAl2007:SSI,
  author  = {Troy D. Sadler AND Sasha A. Barab AND Brianna Scott},
  journal = {Research in Science Education},
  title   = {What Do Students Gain by Engaging in Socioscientific Inquiry?},
  year    = {2007},
  pages   = {371--391},
  volume  = {37},
  doi     = {https://doi.org/10.1007/s11165-006-9030-9},
  groups  = {Socioscientific reasoning},
}

@Book{klafki2007:neueStudien,
  author    = {Wolfgang Klafki},
  publisher = {Beltz},
  title     = {Neue Studien zur Bildungstheorie und Didaktik. Zeitgemäße Allgemeinbildung und kritisch-konstruktive Didaktik},
  year      = {2007},
  address   = {Weinheim},
  edition   = {6., neu ausgestattete Auflage},
}

@Book{kmk2004:bildungsstandardsPhysikAHR,
  author    = {{Sekretariat der Ständigen Konferenz der Kultusminister der Länder in der Bundesrepublik Deutschland (KMK)}},
  publisher = {Carl Link Verlag},
  title     = {Bildungsstandards im Fach Physik für die Allgemeine Hochschulreife},
  year      = {2020},
  address   = {Bonn und Berlin},
}

Minimal non-working example

The preamble is changed to the following:

documentclass[12pt]{scrartcl}

usepackage{ucs}                
usepackage[utf8x]{inputenc}
usepackage[T1]{fontenc}

usepackage[ngerman]{babel}

usepackage{graphicx}
usepackage{caption}
usepackage{subcaption}
usepackage{enumitem}

renewcommand{labelenumi}{theenumi)}

usepackage{amsmath,amssymb,amstext,amsthm}

usepackage[natbibapa]{apacite}
bibliographystyle{apacite}

usepackage{setspace}

usepackage{ulem}

usepackage{geometry}
geometry{a4paper, top=20mm, left=25mm, right=25mm, bottom=20mm,
headsep=5mm, footskip=10mm}

usepackage{booktabs}

usepackage{ebgaramond}
usepackage{AlegreyaSans}

usepackage{hyperref}
hypersetup{hidelinks}

After each change of the packages I deleted all the aux, bbl, blg, log and out-files and compiled it again.
I tried removing all non-necessary packages in the preamble. For one time it worked, but I couldn’t figure out why. I thought the font-packages (ebgaramond and AlegreyaSans) were responsible. After reimplementing them, I got the same error message. So I removed them again but the error stayed.
I tried requiring the apacite package, but that gave me even more errors. Using PassOptionsToPackage{natbibapa}{apacite} also didn’t change anything.
Changing to apacite without natbibapa is not an option because of the huge number of citations in my paper.