
If you are using a VPN or proxy to connect to the Internet, disable them to see if that fixes your problem. Open the App Store on your Mac and then click Store (top menu bar) and click Sing Out and then sing back in. From the top menu bar, click Account and then Sign out.
You’ll know when the service is working again. If this the case, there is little you can do. For instance, currently, it is saying “Mac App Store – Completed Maintenance. 1.7% of users were affected. Customers may have been unable to make purchases from the App Store, iTunes Store, iBooks Store, or Mac App Store.” As you can see, the Mac App Store was down for some users, and but now it is fixed. It is possible that the App Store service is having issues with its servers or systems. Go to Apple’s System Status website and check.
Make sure that Apple Mac App Store servers are up and running. Contact your Internet service provider and confirm that there are no outages. Restart your router/modem (Unplug the power supply, wait 30 seconds and then plug it back in). If not, you may try the following troubleshooting tips: Check to see if websites load in Safari or in other browsers. Make sure that your Mac is connected to the Internet. First, let’s make sure that there are no network connectivity issues. See also: Cannot Send or Receive Messages on Your Mac? Why can’t my Mac connect to the App Store? This article explains what you can do when your Mac can’t connect to the Apple App Store and won’t download, install, or update apps. Please note that if you are having this issue on your iPhone or iPad, please see this article.
Further, users stated that this problem started after updating their Mac devices. Several users have reported that they are having problems connecting to the Mac App Store.