Thank you for contacting Namecheap support!
Please specify the exact domain you would like to use with google apps.
By default cPanel enables our server's IP for SPF record, so you should use this record:
"v=spf1 include:_spf.google.com ~all" instead of "v=spf1 +a +mx +ip4:18.104.22.168 ?all"
It is possible to update SPF records with "email authentication" feature in cPanel or we can change the record for you once you specify all the domains.
Looking forward to hearing from you.