diff --git a/sandbox/Dockerfile b/sandbox/Dockerfile
index 63378fa..0ee4b03 100644
--- a/sandbox/Dockerfile
+++ b/sandbox/Dockerfile
@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
+
 # First Stage: Build Proxy service
-FROM python:3.13-alpine AS deps
+FROM --platform=linux/x86_64 python:3.13-alpine AS deps
 
 # Install poetry
 RUN pip install poetry
@@ -8,7 +10,7 @@ RUN pip install poetry
 COPY pyproject.toml poetry.lock ./
 RUN poetry config virtualenvs.in-project true && poetry install --no-root
 
-FROM deps AS runtime
+FROM --platform=linux/x86_64 deps AS runtime
 
 # Copy virtual env from python-deps stage
 COPY --from=deps /.venv /.venv
@@ -23,17 +25,17 @@ USER appuser
 
 # Install application into container
 COPY app.py __init__.py /home/appuser/app/
+COPY ./specification /home/appuser/app/specification
 # Copy supervisord configuration
 COPY supervisord.conf /etc/supervisord.conf
 
-COPY ./specification /home/appuser/app/specification
-# Install Prism
+# Switch to root and install Prism & Supervisor
 USER root
 RUN apk add --no-cache nodejs npm && \
     npm install --ignore-scripts -g @stoplight/prism-cli && \
     apk add --no-cache supervisor
 
-# Expose ports
+# Expose port and start app
 EXPOSE 9000
 ENV UPSTREAM_HOST=http://localhost:5000
 # Run supervisord
diff --git a/sandbox/Makefile b/sandbox/Makefile
index 07e8c68..c9eb6ff 100644
--- a/sandbox/Makefile
+++ b/sandbox/Makefile
@@ -35,7 +35,7 @@ build-and-publish-sandbox-image:
 
 deploy-sandbox-spec:
 	make -C .. construct-spec APIM_ENV=sandbox
-	proxygen instance deploy sandbox eligibility-signposting-api build/specification/sandbox/eligibility-signposting-api.yaml
+	proxygen instance deploy sandbox eligibility-signposting-api ../build/specification/sandbox/eligibility-signposting-api.yaml
 
 up: build
 	docker compose -f docker-compose.yaml up -d