Dynamic routes in the pages router follow the second convention. If deleting the cached .next folder before starting the dev server doesn't fix your issue then it's likely you have errors in your code.

Thanks I'll try that

@Giant panda , that worked well - thanks.

Now, however, I have another problem. You see, with the app router, I had this folder structure:

app/lessons/[lessonId]/[sessionId]/page.tsx, and at that page I had access to the params from the [lessonId] as well as the params from [sessionId] in the generateStaticParams function. That way I could fetch data for a specific Lesson by its Id, then map out all it's sessions and genereate paths from these slugs.

The setup looked like this:

export async function generateStaticParams({
  params: { lessonId },
}: {
  params: { lessonId: string };
}) {
  const { sessions } = await getLessonBySlug(lessonId);

  return sessions.map((session) => ({
    sessionId: session._key,
  }));
}

async function getLesson(id: string) {
  const res = await getLessonBySlug(id);
  return res;
}

export default async function Session({
  params: { lessonId, sessionId },
}: {
  params: { lessonId: string; sessionId: string };
}) { // rest of the code

Now, in the page router's getStaticPaths it seems I don't have access to the params from the parent route. Is that correct? At least I can't find any docs on it. If that is the case, do you (or anyone else) know how to solve this?

My current route structure can be seen in the screenshot.

Your current folder structure does not have any path that is mapped to what was app/lessons/[lessonId]/[sessionId]/page.tsx in the app router

For that path in particular you'd need a file at pages/lessons/[lessonId]/[sessionId].tsx and the gSP function would need to return both params lessonId and sessionId for which the page exists.

Ok, I see. I moved the [lessonId].tsx to it's own folder, since i thought I could not have a pages/lessons/index.tsx and a pages/lessons/[slug].tsx in the same folder.

Also, I still don't know how/if I can get the route params to use in my getStaticPaths somehow? I can't generate the paths for the sessions, unless I got the specific lessonId from the parent route...