When I try to deploy with a dockerfile and release error buliding: failed to compute cache key

The docker files is here

FROM nginxproxymanager/nginx-full:certbot-node

ARG TARGETPLATFORM
ARG BUILD_VERSION
ARG BUILD_COMMIT
ARG BUILD_DATE

ENV SUPPRESS_NO_CONFIG_WARNING=1 \
	S6_FIX_ATTRS_HIDDEN=1 \
	S6_BEHAVIOUR_IF_STAGE2_FAILS=1 \
	NODE_ENV=production \
	NPM_BUILD_VERSION="${BUILD_VERSION}" \
	NPM_BUILD_COMMIT="${BUILD_COMMIT}" \
	NPM_BUILD_DATE="${BUILD_DATE}"

RUN echo "fs.file-max = 65535" > /etc/sysctl.conf \
	&& apt-get update \
	&& apt-get install -y --no-install-recommends jq logrotate \
	&& apt-get clean \
	&& rm -rf /var/lib/apt/lists/*

# s6 overlay
COPY scripts/install-s6 /tmp/install-s6
RUN /tmp/install-s6 "${TARGETPLATFORM}" && rm -f /tmp/install-s6

EXPOSE 80 81 443

COPY backend       /app
COPY frontend/dist /app/frontend
COPY global        /app/global

WORKDIR /app
RUN yarn install

# add late to limit cache-busting by modifications
COPY docker/rootfs /

# Remove frontend service not required for prod, dev nginx config as well
RUN rm -rf /etc/services.d/frontend /etc/nginx/conf.d/dev.conf

# Change permission of logrotate config file
RUN chmod 644 /etc/logrotate.d/nginx-proxy-manager

# fix for pip installs
# https://github.com/NginxProxyManager/nginx-proxy-manager/issues/1769
RUN pip uninstall --yes setuptools \
	&& pip install "setuptools==58.0.0"

VOLUME [ "/data", "/etc/letsencrypt" ]
ENTRYPOINT [ "/init" ]

LABEL org.label-schema.schema-version="1.0" \
	org.label-schema.license="MIT" \
	org.label-schema.name="nginx-proxy-manager" \
	org.label-schema.description="Docker container for managing Nginx proxy hosts with a simple, powerful interface " \
	org.label-schema.url="https://github.com/jc21/nginx-proxy-manager" \
	org.label-schema.vcs-url="https://github.com/jc21/nginx-proxy-manager.git" \
	org.label-schema.cmd="docker run --rm -ti jc21/nginx-proxy-manager:latest"

and here is the fly.toml

# fly.toml file generated for npm on 2023-02-27T22:56:18+08:00

app = "tokman"
kill_signal = "SIGINT"
kill_timeout = 5
processes = []

[build]
  [build.args]
    MIX_ENV = "staging"

[env]

[experimental]
  allowed_public_ports = []
  auto_rollback = true

[[services]]
  http_checks = []
  internal_port = 8080
  processes = ["app"]
  protocol = "tcp"
  script_checks = []
  [services.concurrency]
    hard_limit = 25
    soft_limit = 20
    type = "connections"

  [[services.ports]]
    force_https = true
    handlers = ["http"]
    port = 80

  [[services.ports]]
    handlers = ["tls", "http"]
    port = 443

  [[services.tcp_checks]]
    grace_period = "1s"
    interval = "15s"
    restart_limit = 0
    timeout = "2s"

when I try to run the command, it show the log below:

 Would you like to deploy now? Yes
==> Building image
Remote builder fly-builder-winter-wind-2303 ready
==> Creating build context
--> Creating build context done
==> Building image with Docker
--> docker host: 20.10.12 linux x86_64
[+] Building 88.5s (0/1)                                                                                                                                                                          
[+] Building 6.0s (9/16)                                                                                                                                                                          
 => [internal] load remote build context                                                                                                                                                     0.0s
 => copy /context /                                                                                                                                                                          0.1s
 => [internal] load metadata for docker.io/nginxproxymanager/nginx-full:certbot-node                                                                                                         4.1s
 => CANCELED [ 1/13] FROM docker.io/nginxproxymanager/nginx-full:certbot-node@sha256:3bf83992ba055ede599290d90782dec32b5edac7ba18881f3942b902ccf62890                                        0.0s
 => => resolve docker.io/nginxproxymanager/nginx-full:certbot-node@sha256:3bf83992ba055ede599290d90782dec32b5edac7ba18881f3942b902ccf62890                                                   0.0s
 => => sha256:3bf83992ba055ede599290d90782dec32b5edac7ba18881f3942b902ccf62890 990B / 990B                                                                                                   0.0s
 => => sha256:b09eb247e0d3ebdaa1471ff80832aae7a4f18177c9654609ac86ed4b5c6c38c2 4.43kB / 4.43kB                                                                                               0.0s
 => => sha256:ad5f780da3030715782f7b1a3058bde47b6bb5385486b8480aa76c13067e8aca 10.79kB / 10.79kB                                                                                             0.0s
 => CACHED [ 2/13] RUN echo "fs.file-max = 65535" > /etc/sysctl.conf  && apt-get update  && apt-get install -y --no-install-recommends jq logrotate  && apt-get clean  && rm -rf /var/lib/a  0.0s
 => CACHED [ 3/13] COPY scripts/install-s6 /tmp/install-s6                                                                                                                                   0.0s
 => CACHED [ 4/13] RUN /tmp/install-s6 "linux/amd64" && rm -f /tmp/install-s6                                                                                                                0.0s
 => CACHED [ 5/13] COPY backend       /app                                                                                                                                                   0.0s
 => ERROR [ 6/13] COPY frontend/dist /app/frontend                                                                                                                                           0.0s
------
 > [ 6/13] COPY frontend/dist /app/frontend:
------
Error failed to fetch an image or build from source: error building: failed to compute cache key: "/frontend/dist" not found: not found

I am a fresher in fly.io, and honestly I don’t know where the error come from, hope you can help me to fix it. Cheerrrrs!!