You can use a Pushpad account to add web push notifications to multiple domains.
If you have multiple websites and they are not related, then you should create a sender for each website. You can create multiple senders inside one account or use multiple accounts if you prefer.
For example, if you have a website about cars and onother about apples, then you should create two different senders for better separation and security.
Same project, multiple domains
If you have multiple domains that belong to the same application or that are strictly related, then you can use one sender for all the domains. You can configure a sender to support multiple domains: go to sender settings to add additional domains (or subdomains).
For example, if your website supports multiple languages, you may have a domain name for each language. In that case you can use the same sender for all the domains.
Wildcard subdomains or any domain
Safari does not support this feature. You can drop support for Safari or use another method.
If you have a website or web app that consists of many different subdomains or domains, then you can use one sender for all the subdomains / domains. You don't need any configuration: when you create the sender enter the name of your main domain and then you can use the sender with any subdomain / domain.
For example, if you have a multi tenant web app that use a different subdomain / domain for each customer, then you can easily add push notifications to all subdomains / domains using just one sender. However your customers cannot export their data, because you use the same key pair for everyone (see "Different websites" for an alternative).