Uploading files fails when behind a reverse proxy

When we try to upload a file to a kotahi behind a reverse proxy, it fails because it sends the request to localhost:4000/convertDocxToHTML

OPTIONS /convertDocxToHTML HTTP/1.1
Host: localhost:4000
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Access-Control-Request-Method: POST
Access-Control-Request-Headers: authorization
Origin: https://kotahitesting.cloud68.co
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

This is our env

DOCKER_BUILDKIT=1
COMPOSE_DOCKER_CLI_BUILD=1
NODE_ENV='production'
POSTGRES_USER='kotahi_user'
POSTGRES_PASSWORD='*'
POSTGRES_HOST='********'
POSTGRES_DB='kotahi'
POSTGRES_PORT='5432'
PUBSWEET_SECRET='*'
ORCID_CLIENT_ID='APP-GZ79X******'
ORCID_CLIENT_SECRET='*'
SERVER_PORT='3050'
SERVER_HOST='127.0.0.1'
SERVER_PROTOCOL=http
CLIENT_PROTOCOL=https
CLIENT_HOST=kotahitesting.cloud68.co
CLIENT_PORT=
PUBLIC_CLIENT_PROTOCOL=https
PUBLIC_CLIENT_HOST=kotahitesting.cloud68.co
PUBLIC_CLIENT_PORT=
S3_ACCESS_KEY_ID=*
S3_ACCESS_KEY_SECRET=*
S3_ENDPOINT=https://******-s3.cloud68.co
INSTANCE_NAME=aperture

Looking at https://gitlab.coko.foundation/kotahi/kotahi/-/blob/main/Dockerfile-production#L22, it seems the values are hardset?