docker c-up says Manifold_tag no Cmdlet

[GerhardMes]

By starting docker-compose as mentioned in the docs including the manifold_tag before, I get the following error (On Windows)
(the version is the same as in the manifold_version file)

CategoryInfo: ObjectNot Found: (Manifold_tag=v8.1.2-beta.4 docker-compose up -d
FullyQualifiedErrorID: Command not found Exception.

Above it says that the manifold_tag is not recognised as Cmdlet, function, script or executable program.

Any idea what this causes this error?
Thanks