BUG: if all ports are used, backend returns port as 0 instead of an error

[viggy28]

@rajatmaheshwari2512 noted the following:
https://spinuphost.slack.com/files/U025XKBM6LW/F029MUSNZB7/image.png?origin_team=T023Q4EGCA0&origin_channel=C024J8CTW06