Here's a Python script that reads all of the domains from your WebFaction account and adds them to your Opalstack account if they don't exist already:

#!/bin/env python3

import requests
from xmlrpc.client import ServerProxy

WF_USER = 'your webfaction username'
WF_PASS = 'your webfaction password'
OPAL_TOKEN = 'your opalstack API token'

OPAL_HEADERS = {
    'Authorization': f'Token {OPAL_TOKEN}',
    'Content-Type':'application/json'
}

wf = ServerProxy('https://api.webfaction.com/')
wf_session, wf_account = wf.login(WF_USER,WF_PASS)
wf_domains = wf.list_domains(wf_session)

opal_domains = requests.get(
    'https://my.opalstack.com/api/v0/domain/list/',
    headers=OPAL_HEADERS
).json()['domains']

opal_domain_names = [d['name'] for d in opal_domains]

for d in wf_domains:
    if d['domain'] not in opal_domain_names:
        print(f'adding {d["domain"]}')
        payload = [{'name': d['domain']}]
        r = requests.post('https://my.opalstack.com/api/v0/domain/add/',
                        headers=OPAL_HEADERS,
                        json=payload
        )
        print(r.json())
    for s in d['subdomains']:
        subdomain = f'{s}.{d["domain"]}'
        if subdomain not in opal_domain_names:
            print(f'adding {subdomain}')
            payload = [{'name': subdomain}]
            r = requests.post('https://my.opalstack.com/api/v0/domain/add/',
                            headers=OPAL_HEADERS,
                            json=payload
            )
            print(r.json())

To use it:

Get an Opalstack API token from https://my.opalstack.com/tokens/ if you don't have one already.
Copy the script and save it into a python file like import_domains.py on your Opalstack shell user account (or on your own computer if you have Python 3 with the requests library installed).
Edit the script to put in your own API token and WebFaction credentials.
Run it like: python3 import_domains.py

Easy peasy, give it a try and let me know how it goes 🙂