Error: No such container:path: when trying to use cp in shell script

[admin]

I have a script that makes a directory inside a docker container and copies a file from the host to the new directory.

# $wpc is a variable holding the container name
#make the directory in the container
docker exec $wpc bash -c "mkdir -p /root/.ssh"
#stop container 
docker stop $wpc
#copy file to container
docker cp  ~/.ssh/id_rsa $wpc:/root/.ssh/id_rsa
# wait until the wordpress container is running 
docker start $wpc

but I get this error:

Error: No such container:path: <container_name>:\root\.ssh

Is the syntax wrong? I tried changing the permissions for the folder before the file is copied, with no luck.

I'm running docker on windows server 2019 and My Docker Info:

Client: Docker Engine - Enterprise
 Version:           19.03.5
 API version:       1.40
 Go version:        go1.12.12
 Git commit:        2ee0c57608
 Built:             11/13/2019 08:00:16
 OS/Arch:           windows/amd64
 Experimental:      true

Server: Docker Engine - Enterprise
 Engine:
  Version:          19.03.5
  API version:      1.40 (minimum version 1.24)
  Go version:       go1.12.12
  Git commit:       2ee0c57608
  Built:            11/13/2019 07:58:51
  OS/Arch:          windows/amd64
  Experimental:     true

Any help or info appreciated.