Specifying prefix in opam file - ocaml

Question

I have an opam file with the line:
install: [make "install" "prefix=${prefix}$"]
my intent is that something like the following (which I have tested) will be executed by opam install:
make install prefix=/home/laheadle/.opam/4.02.0
In the Makefile I have:
install: js
cp ./tournabox.css ./tournabox.js $(prefix)/lib
But I get the error:
#=== ERROR while installing tournabox.1.0 =====================================#
# opam-version 1.2.0
# os linux
# command make install prefix=${prefix}$
# path /home/laheadle/.opam/4.02.0/build/tournabox.1.0
# compiler 4.02.0
# exit-code 2
# env-file /home/laheadle/.opam/4.02.0/build/tournabox.1.0/tournabox-7593-d2c37b.env
# stdout-file /home/laheadle/.opam/4.02.0/build/tournabox.1.0/tournabox-7593-d2c37b.out
# stderr-file /home/laheadle/.opam/4.02.0/build/tournabox.1.0/tournabox-7593-d2c37b.err
### stdout ###
# ocamlbuild -cflag -annot -use-ocamlfind -pkgs js_of_ocaml.log,js_of_ocaml,js_of_ocaml.syntax -syntax camlp4o tournabox.byte
# js_of_ocaml +weak.js tournabox.byte
# lessc tournabox.less tournabox.css
# ocamlbuild -cflag -annot -use-ocamlfind -pkgs js_of_ocaml.log,js_of_ocaml,js_of_ocaml.syntax -syntax camlp4o tournabox.byte
### stderr ###
# make: *** Recursive variable `prefix' references itself (eventually). Stop.
What am I doing wrong?

Answer 1

OPAM uses %{prefix}%, not ${prefix}$.
You can see the use of prefix in Creating OPAM Packages part of the docs.

Answer 2

This error msg seems printed by make:
‘Recursive variable `xxx' references itself (eventually). Stop.’
This means you’ve defined a normal (recursive) make variable xxx that, when it’s expanded, will refer to itself (xxx). This is not allowed; either use simply-expanded variables (‘:=’ or ‘::=’) or use the append operator (‘+=’). See How to Use Variables.
https://www.gnu.org/software/make/manual/html_node/Error-Messages.html