opam install ocaml-lsp-server is not working

trying to install, but getting the following message.

 Constructing initial basis... The following dependencies couldn't be met: - ocaml-lsp-server → dyn → ocaml >= 4.08.0      base of this switch (use `--unlock-base' to force) - ocaml-lsp-server → ocaml >= 4.06      base of this switch (use `--unlock-base' to force) - ocaml-lsp-server → pp >= 1.1.2 → ocaml >= 4.08.0      base of this switch (use `--unlock-base' to force) No solution found, exiting

Could anyone tell me how to install ocaml-lsp-server? Thanks in advance!