Reconnecting your account would be the first troubleshooting step for any error related to the social media account and failed posts. This generates the API token all over again and refreshes the connection fully, often solving post publishing and interaction pulling errors, just to name a few.
In order to complete that, please do the following:
Disconnect your social media account by clicking the red X.
Once you do that, you can reconnect from scratch, and this should reset your connection:
Here are a couple of tips:
You can use Manage Social Accounts to disconnect, refresh, and connect Social Accounts.
You can also view any Social Account that requires attention due to failures or expiration from here.
Any failed connections can be connected directly in Post Builder.