docker-compose version

At home on my Mac I use Docker Compose to build the combined nginx + gunicorn containers.
In the file proofofconcept/v7_pickle_web_interface/docker-compose.yaml
I had
version: "3.7"
which worked for me.
(The compatibility matrix is here: https://docs.docker.com/compose/compose-file/)

I ran docker-compose on DigitalOcean's 18.04 Ubuntu and got the message

$ docker-compose up --build --remove-orphans
ERROR: Version in "./docker-compose.yaml" is unsupported. 

The versions on DigitalOcean's Ubuntu 18.04 are

$ docker version
Client: Docker Engine - Community
 Version:           19.03.8

$ docker-compose version
docker-compose version 1.21.2, build a133471
docker-py version: 3.3.0
CPython version: 3.6.5
OpenSSL version: OpenSSL 1.0.1t  3 May 2016

while at home I have

$ docker version
Client: Docker Engine - Community
 Version:           19.03.8

$ docker-compose version
docker-compose version 1.25.4, build 8d51620a
docker-py version: 4.1.0
CPython version: 3.7.5
OpenSSL version: OpenSSL 1.1.1d  10 Sep 2019

The fix was to change the docker-compose.yaml line to
version: "3.7"