Some google plus business pages are not visible to add a new post under the brand accounts and it can be very frustrating. However, when you post using third party tools like Hootsuite, it works fine.
So, this is what you need to do.
Login to your google plus and in top right-hand side click on the photo icon and see if you can find your brand account link. If you will then it should work fine.
If you do not see then just copy and paste in the browser where you have logged in with right account and it will show you your brand accounts.