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I've been researching for days about this problem.

I was upgrading scala version of my project from 2.12.15 to 2.13.8, in the meantime I upgraded spray-json from 1.3.4 to 1.3.6. akka-http-spray-json is still 10.2.7.

Within building there are multiple places that have errors, all of them are related as[List], the code is like:

var route: Route =
    (path("test-path") & post) {
        entity(as[List[MyCaseClass]]) { reqs =>
          ......
          ......

The error showed:

could not find implicit value for parameter um: akka.http.scaladsl.unmarshalling.FromRequestUnmarshaller[List[MyCaseClass]]

I saw the akka-http source code has no change logs about it, also scala 2.13.x has no change logs about it. Why does as suddenly not accept List type, not accept Seq or Array also?

Hustwhw
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  • Does this answer your question? [akka-http error: could not find implicit value for parameter um: akka.http.scaladsl.unmarshalling.FromRequestUnmarshaller](https://stackoverflow.com/questions/33663732/akka-http-error-could-not-find-implicit-value-for-parameter-um-akka-http-scala) – 0x263A Jun 08 '22 at 20:41
  • @0x263A Thanks, but I don't think it can solve my issue. I've already tried their solutions but didn't work. The key to my issue is, that only the `List` of something cannot be unmarshalled, I don't know why. – Hustwhw Jun 09 '22 at 17:16

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