rstudio server and Google Cloud Engine: add user with googleComputeEngineR gce_rstudio_adduser() function

RE: instantiating an Rstudio vm with Google GCP and googleComputeEngineR package

An RStudio server instance was created according to the gce_vm() function of the googleComputeEngineR package.

The gce_rstudio_adduser() function was subsequently invoked to add users.

The vm attributes are as follow;

==Google Compute Engine Instance==

Name:                rstudio-sm
Created:             2018-10-11 08:48:55
Machine Type:        n1-highmem-2
Status:              RUNNING
Zone:                us-east4-c
External IP:         xx.xx.xx.xx
Disks: 
            deviceName       type       mode boot autoDelete
1 rstudio-sm-boot-disk PERSISTENT READ_WRITE TRUE       TRUE

When the gce_rstudio_adduser() function is run as follow:

gce_rstudio_adduser(vm, username = "ProfCalculus", password = "strngpasswd")

it returns:

Auto-refreshing stale OAuth token.
==Google Compute Engine Instance==

Name:                rstudio-sm
Created:             2018-10-11 08:48:55
Machine Type:        n1-highmem-2
Status:              RUNNING
Zone:                us-east4-c
External IP:         xx.xx.xx.xx
Disks: 
            deviceName       type       mode boot autoDelete
1 rstudio-sm-boot-disk PERSISTENT READ_WRITE TRUE       TRUE`

This new created credential does not allow to sign in to the Rstudio resource.
The following error message is instead returned
Error: Incorrect or invalid username/password

Thanks in advance for any guidance
Manuel