To create a Push-certificate for iOS app, go to the Certificates menu in the Apple Developer
In the side menu, click the Certificates submenu - Production
And click on the "+" icon to add the certificate
In the menu that opens, select the "Apple Push Notification service SSL (Sandbox & Production)"
Later in the drop-down menu, select the application for which you need a Push-certificate
After performing these actions, you will be prompted to create a certificate request on your Mac.
To do this, go to "Keychain Access" on your Mac.
In the application menu "Keychain Access", go to the menu "Certificate Assistant".
And select "Request a certificate from a Certificate Authority".
In the menu that opens, fill in the fields (Email, and Common Name), and mark the "Save to disk".
In the next window, select where to save the certificate.
Next, return to the site and select the newly created certificate request.
Now you can download your Push-certificate