What happens if the seller refuses to hand over logins and passwords after closing?

If delivering this kind of access was part of what the seller was required to hand over under the purchase agreement — commonly listed as a closing deliverable or set out as an express post-closing covenant — refusing to do so is a breach of that specific obligation. The buyer generally has remedies for this, including seeking a court order compelling delivery of the actual information, since what's needed here is the access itself rather than simply money, alongside a damages claim for any loss the delay causes.

Because operational disruption from lost access to accounts, systems, or platforms can escalate quickly, document the request and the refusal in writing right away and get legal advice promptly rather than waiting to see if the seller comes around. If the purchase agreement never actually addressed handing over this kind of access at all, your position is weaker and depends on whether it can be shown to fall within a broader description of purchased assets or deliverables already in the agreement.