diff --git a/Dockerfile b/Dockerfile
index d95a8da..5adb7b4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -3,5 +3,5 @@ WORKDIR /action
 RUN gem install jwt && \
     apk add jq && \
     apk add curl
-COPY generate-jwt.rb get-installation-access-token.sh ./
-ENTRYPOINT ["/action/get-installation-access-token.sh"]
\ No newline at end of file
+COPY generate_jwt.rb get-installation-access-token.sh ./
+ENTRYPOINT ["/action/get-installation-access-token.sh"]
diff --git a/generate-jwt.rb b/generate_jwt.rb
similarity index 59%
rename from generate-jwt.rb
rename to generate_jwt.rb
index d9e33e7..81ec073 100644
--- a/generate-jwt.rb
+++ b/generate_jwt.rb
@@ -1,11 +1,15 @@
+# frozen_string_literal: true
+
 require 'openssl'
 require 'jwt'
 
 private_key = ENV.fetch('PRIVATE_KEY')
 app_id = ENV.fetch('APP_ID')
 
-puts JWT.encode({
+payload = {
   iat: Time.now.to_i,
   exp: Time.now.to_i + (10 * 60),
   iss: app_id
-}, OpenSSL::PKey::RSA.new(private_key), 'RS256')
\ No newline at end of file
+}
+
+puts JWT.encode(payload, OpenSSL::PKey::RSA.new(private_key), 'RS256')
diff --git a/get-installation-access-token.sh b/get-installation-access-token.sh
index 959fe0f..cc922b2 100755
--- a/get-installation-access-token.sh
+++ b/get-installation-access-token.sh
@@ -3,27 +3,26 @@ export PRIVATE_KEY=${1:?Usage: ${0} <private-key> <app-id>}
 export APP_ID=${2:?Usage: ${0} <private-key> <app-id>}
 repo=${GITHUB_REPOSITORY:?Missing required GITHUB_REPOSITORY environment variable}
 
-[[ ! -z "$INPUT_REPO" ]] && repo=$INPUT_REPO
+[ -n "$INPUT_REPO" ] && repo="$INPUT_REPO"
 
-jwt=$(ruby $(dirname $0)/generate-jwt.rb)
-installation_id=$(curl -s \
--H "Authorization: Bearer ${jwt}" \
--H "Accept: application/vnd.github.v3+json" \
-https://api.github.com/repos/${repo}/installation | jq -r .id)
+jwt=$(ruby "$(dirname "$0")"/generate_jwt.rb)
+response=$(curl -s -H "Authorization: Bearer ${jwt}" -H "Accept: application/vnd.github.v3+json" "https://api.github.com/repos/${repo}/installation")
+installation_id=$(echo "$response" | jq -r .id)
 
 if [ "$installation_id" = "null" ]; then
-  echo "Unable to get installation ID. Is the GitHub App installed on ${repo}?"
-  exit 1
+    echo "Unable to get installation ID. Is the GitHub App installed on ${repo}?"
+    echo "$response" | jq -r .message
+    exit 1
 fi
 
 token=$(curl -s -X POST \
--H "Authorization: Bearer ${jwt}" \
--H "Accept: application/vnd.github.v3+json" \
-https://api.github.com/app/installations/${installation_id}/access_tokens | jq -r .token)
+             -H "Authorization: Bearer ${jwt}" \
+             -H "Accept: application/vnd.github.v3+json" \
+             https://api.github.com/app/installations/"${installation_id}"/access_tokens | jq -r .token)
 
 if [ "$token" = "null" ]; then
-  echo "Unable to generate installation access token"
-  exit 1
+    echo "Unable to generate installation access token"
+    exit 1
 fi
 
-echo ::set-output name=token::${token}
+echo "::set-output name=token::${token}"