It's important to understand the terminology used as a Google Account can be linked to one or more Google services. Facebook is excluded from this conversation as it does not have the same complexity.
Google Account - This is the Email address and password that you login to Google Services with. This can be an email address with a custom domain or gmail address.
Google Service - This refers to the Google owned applications, such as Google Ads, Google Analytics, Google Search Console or Google My Business.
How to fix a connection that has an error
There are several types of errors that can occur with your connections.
Account Errors - Authentication tokens are used to securely access your data which constantly expire and therefore need to be refreshed periodically. The authentication can b revoked or have an error refreshing, which break the connection. If this occurs you will be sent an email informing you that you will need to connect again. Please follow the Google Account error steps below to re-establish the connection.
Service Errors - Permissions and settings on your Accounts can change over time and can cause errors in connecting to the Service. For example if you setup a Client that uses a particular Google Analytics Property (View) and that gets changes deleted in favour of another one. Any connected features will break and require you to remove anything connected to it and then reconnect.
To fix a Service error you will need to Delete or Archive any Active Jobs (KPIs, Budget, Automations, Anomalies) and then update the settings.
Google Account Error
To fix an Account connection which has an error, click on the 3 dot menu (also called overflow menu) and then click Reconnect. You will need to complete the Auth process again and sometimes a refresh of the page is required as all linked jobs (KPIs, Budgets) to be updated.