Why the contract has to deal with them.
For many businesses the domain, the website, the business email addresses and the social accounts are among the most valuable assets and the main marketing tools, so the sale agreement should deal with transferring them rather than leaving it to chance.
What varies by platform.
A domain is transferred through the registrar, usually needing the current registrant, often the seller, and sometimes an authorisation code, with steps that differ between registrars. A website needs hosting access and a decision about what data comes with it, such as past sales and customer history, which should be specified in the agreement. Email addresses usually depend on owning the domain. Social accounts are the most uneven. Some, such as a Facebook page or a LinkedIn page, are handled by changing administrators rather than a true transfer, and a new Facebook administrator cannot make changes for a short initial period, so the handover has to be planned. A YouTube channel can be transferred only if it is linked to a brand account rather than a personal one. LinkedIn's own terms say the agreement cannot be assigned, X is silent and a transfer by passing login details carries a cancellation risk, and Instagram prohibits selling or transferring an account altogether. Where transfer is not possible, the only route may be for the seller to close the account and the buyer to open a new one, losing the followers and reviews.
A share sale is different.
If the sale is a share sale, where the company stays the account holder, most of this falls away because the owner of the accounts has not changed. Special conditions are often used to pin down who does what and by when. We cover digital asset transfer in the contract through our business sale and purchase service.
Some platforms forbid transferring an account at all, and others only allow an administrator change with a waiting period. Where an account cannot move, closing and reopening may be the only path, and the business can lose its followers and reviews, so plan it before settlement.