An access token is a temporary credential that lets an app call an API on your behalf. It is what a platform issues after you approve an OAuth consent screen, and it carries exactly the permissions you granted, nothing more.
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Tokens expire
Access tokens have lifetimes. Some last an hour, some last weeks, and platforms often pair them with a refresh mechanism that swaps an aging token for a fresh one. When a token can no longer be refreshed, for example after a password change or a revoked permission, the connection breaks and the account has to be reconnected. That is what "reconnect your account" means in any social tool: the old grant died, and the platform needs you to approve a new one. InvisibleAPI refreshes Instagram tokens automatically and gives you a reconnect flow when a grant expires.
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Access tokens versus API keys
An API key identifies an application and typically lives until someone revokes it. An access token represents a specific user's permission and expires on its own. Social publishing usually involves both: your API key proves who your app is, while each connected account has its own token proving the user said yes.
Go from the definition to the docs that show how to apply it.
Primary solution Reconnect and scopes