Using Safari you will have to manually create a certificate and upload it here.
This can be done within 5 minutes, however, a fee-based Apple Developer Account will be required for that (approx. 99 USD per year). Unfortunately due to technical reasons we cannot run all channels on our account.
How to proceed with an Apple Developer account:
Step 1: Log into the Apple Developer Portal.
Step 2: Navigate to section Certificates, Identifiers & Profiles.
Step 3: Now first create a new "website push ID" under the item "Identifiers". For the identifier best use your reversed domain with the web.-prefix, e.g. example.com becomes web.com.example.
Step 4: Now create a new certificate for your website. Open your keychain access on your Mac for that. Then click keychain assistant -> Request a certificate of a certification authority. Type in your e-mail-address and a name. This general name is only used as a reference, for example "Safari certificate example.com". Select Save to hard disk and click Proceed.
Step 5: Now switch to the Apple Developer portal again and select the just created website push ID. Click edit, then Create certificate and now Continue.
Step 6: Select the file, created by the Keychain access, by clicking Choose file... .
Step 7: You now have successfully created your certificate. Only a few more steps until you can send Safari messages. Now download the certificate (.cer) by clicking Download and open it to import it into the keychain access.
Step 8: In the keychain access please select the login keychain, then click on the category My certificates on the bottom left and search for Website push. Export the certificate with a right click on the certificate and a click on Export in the Personal Information Exchange Format (.P12).
Make sure that you don't enter a password for the certificate.
Step 9: This .P12 file can now be uploaded in your domain settings on CleverPush. Don't forget to also put in your Website Push ID.