Mautic 3 on Dokku - persistent volume?

Your software
My Mautic version is: 3.3.3
My PHP version is: 7.3.27
My Database type and version is: Mysql 5.7

Your problem
I’m attempting to set up Mautic (GitHub - mautic/docker-mautic: Docker Image for Mautic) on Dokku. I have everything working well except for the mounted volume. Mautic stores config files in the volume, so every time the container restarts it needs to be reconfigured if the volume is not set up. The instructions on the above page are:

$ docker volume create mautic_data

$ docker run --name mautic -d \
    --restart=always \
    -e MAUTIC_DB_HOST= \
    -e MAUTIC_DB_USER=root \
    -e MAUTIC_DB_PASSWORD=mypassword \
    -e MAUTIC_DB_NAME=mautic \
    -e MAUTIC_RUN_CRON_JOBS=true \
    -p 8080:80 \
    -v mautic_data:/var/www/html \

I created a persistent volume with dokku using
dokku storage:mount mautic /var/lib/dokku/data/storage/mautic:/mautic_data

this looks fine:

root@apps:/var/lib# dokku storage:report mautic
=====> mautic storage information
    Storage build mounts:                                   
    Storage deploy mounts:         -v /var/lib/dokku/data/storage/mautic:/mautic_data 
   Storage run mounts:            -v /var/lib/dokku/data/storage/mautic:/mautic_data 

However the config is not saved. When restarting the container I get " Mautic not found in /var/www/html - copying now…" and “Writing initial Mautic config” so the volume is not seen

Any ideas on how to mount the store correctly under Dokku?