missing Cats Functor[Future] instance

By importing cats.implicits._ you are actually already importing cats.syntax.AllSyntax and cats.instances.AllInstances

Try using just those imports:

import cats.data._
import cats.implicits._

or (according to your needs):

import cats.data._
import cats.instances.future._

or more specifically:

import cats.data._
import cats.instances.future.catsStdInstancesForFuture

you may also need:

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

Note: of course you have to implicitly provide an actual ExecutionContext in a production environment.

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