Loading mpi modules in Azure Batch with Ubuntu-hpc image

I am trying to set up a multi-instance job using the ubuntu-hpc VM, so that I can use openmpi and RDMA (I was told the limitation of using Intel MPI is not there anymore).

However, this requires the module mpi/openmpi to be loaded ro make the correct version of mpi available (4.1.0 instead of the ubuntu default). When I try to load it when setting up a job or a task, I receive an error saying the module command is not found (it is available if I add a user and log into the node via SSH, but it won't execute if I use issue to the command in a task or job preparation task).

Any help is appreciated. Thanks!