i have problem about IPv6

[BTFKM]

hi,
i wanna use fastapi on both IPv6 and IPv4 network, but i found that
uvicorn api_server:app --host 0.0.0.0 --port 9003 not work on IPv6 and
uvicorn api_server:app --host '::' --port 9003 not work on IPv4.
so a creat a bash:
uvicorn api_server:app --host 0.0.0.0 --port 9003&
uvicorn api_server:app --host '::' --port 9003
for now, its working!
but when i add -- workers 3, the error come out:
uvicorn api_server:app --host 0.0.0.0 --port 9003 --workers 3 &
uvicorn api_server:app --host '::' --port 9003 --workers 3
one of the process error: ERROR: [Errno 98] Address already in use

anyone know how to run both IPv6 and IPv4 with --workers ?