Where the licence key goes
Your Licence Key goes in exactly one place: Addons → Addon Modules → hTech IDrive e2 Tools → Settings — WHMCS's own configuration form for the addon, not this module's own Settings page. Enter it there and save.
This module's own Settings page (reached from inside the addon itself) deliberately says as much, so you are not left looking for the field in the wrong place:
Everything else this module is configured with — your storage tiers, your region allow-list, your retention window, your overage policy and your update manifest address — lives on that second page, not the licence form.
What a valid licence covers
One licence covers one WHMCS installation, keyed to the domain that installation runs on. A domain and its www. form count as one domain, not two. Validation is checked against hTech's licence server, which is sent your licence key together with your installation's domain, IP address and directory.
If you move the installation to a different domain, server or directory, that is a reissue rather than something the licence self-heals — contact hTech to have your key reissued against the new details.
What the licence gates, and what it never touches
This is the part worth reading closely, because it is deliberate rather than an oversight: a licence check that cannot reach hTech's server never suspends, terminates or degrades storage that is already provisioned. The licence gates only the Update page's download step and what is displayed about your licence status on the tools page.
Provisioning a new order, suspending, unsuspending, terminating, collecting usage, the client area, and all three of this module's scheduled passes run on any licence verdict — ours up or down. The reasoning is symmetric with how updates behave (see the article on how updating works): wherever "do nothing" is the safe answer for your customers, that is what this module does, licence server reachable or not.
If your licence lapses entirely, the copy you already have installed keeps working and keeps serving your customers. What lapses is your right to new versions and to support, not what is already running.
If you need help with a licence key
Module support is reached from hTech's support form, with your licence key to hand.