Error attempting to mix deps.get

I attempted to run mix deps.get on localhost and got the following error:

** (Mix.Config.LoadError) could not load config config/config.exs
    ** (KeyError) key "SECRET_KEY_BASE" not found in: %{"Apple_PubSub_Socket_Render" => "/private/tmp/com.apple.launchd.PMeC85gCK2/Render", 
"BINDIR" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang/erts-9.2/bin", 
"COLORFGBG" => "15;0", "COLORTERM" => "truecolor", "EMU" => "beam", 
"HOME" => "/Users/Admin", "ITERM_PROFILE" => "Default", 
"ITERM_SESSION_ID" => "w0t2p0:0F4769CC-83F4-41C0-9F42-9B4F34149B95", 
"LANG" => "en_GB.UTF-8", "LOGNAME" => "Admin", "PATH" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang/erts-9.2/bin:/usr/local/Cellar/erlang/20.2.2/lib/erlang/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin", "PROGNAME" => "erl", "PWD" => "/code/github-backup", 
"ROOTDIR" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang", "SHELL" => "/bin/bash", "SHLVL" => "1", "SSH_AUTH_SOCK" => "/private/tmp/com.apple.launchd.46QiqVHC0d/Listeners", 
"TERM" => "xterm-256color", "TERM_PROGRAM" => "iTerm.app", "TERM_PROGRAM_VERSION" => "3.1.5", "TERM_SESSION_ID" => "w0t2p0:0F4769CC-83F4-41C0-9F42-9B4F34149B95", 
"TMPDIR" => "/var/folders/0m/hlrnvx6n5qv001qcm6x9ny440000gn/T/", "USER" => "Admin", "XPC_FLAGS" => "0x0", "XPC_SERVICE_NAME" => "0", "__CF_USER_TEXT_ENCODING" => "0x1F5:0x0:0x2"}
    (stdlib) :maps.get("SECRET_KEY_BASE", 
%{"Apple_PubSub_Socket_Render" => "/private/tmp/com.apple.launchd.PMeC85gCK2/Render", "BINDIR" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang/erts-9.2/bin", 
"COLORFGBG" => "15;0", "COLORTERM" => "truecolor", "EMU" => "beam", "HOME" => "/Users/Admin", "ITERM_PROFILE" => "Default", 
"ITERM_SESSION_ID" => "w0t2p0:0F4769CC-83F4-41C0-9F42-9B4F34149B95", 
"LANG" => "en_GB.UTF-8", "LOGNAME" => "Admin", "PATH" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang/erts-9.2/bin:/usr/local/Cellar/erlang/20.2.2/lib/erlang/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin", "PROGNAME" => "erl", "PWD" => "/code/github-backup", "ROOTDIR" => "/usr/local/Cellar/erlang/20.2.2/lib/erlang", "SHELL" => "/bin/bash", 
"SHLVL" => "1", "SSH_AUTH_SOCK" => "/private/tmp/com.apple.launchd.46QiqVHC0d/Listeners", "TERM" => "xterm-256color", "TERM_PROGRAM" => "iTerm.app", "TERM_PROGRAM_VERSION" => "3.1.5", "TERM_SESSION_ID" => "w0t2p0:0F4769CC-83F4-41C0-9F42-9B4F34149B95", 
"TMPDIR" => "/var/folders/0m/hlrnvx6n5qv001qcm6x9ny440000gn/T/", "USER" => "Admin", "XPC_FLAGS" => "0x0", "XPC_SERVICE_NAME" => "0", "__CF_USER_TEXT_ENCODING" => "0x1F5:0x0:0x2"})
    (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6
    (stdlib) erl_eval.erl:878: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:236: :erl_eval.expr/5
    (stdlib) erl_eval.erl:228: :erl_eval.expr/5
    (stdlib) erl_eval.erl:229: :erl_eval.expr/5
    (stdlib) erl_eval.erl:878: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:236: :erl_eval.expr/5

I'm re-reading the Docs (README) to see if I "missed a step" ...