Most problems have a short answer, so the common ones are here rather than behind a contact form.
It was in your purchase email. If that is gone, reply to the receipt from the payment provider and the key can be reissued — it is generated from your order, not stored in an account.
Yes. There is no activation check and nothing counts installs. Paste the same key wherever you use the extension.
Paste the whole key, including the full stop in the middle. A key for one of the four extensions will not work in the others.
System audio is shared by the browser only if you tick the box in its own sharing dialog when you pick what to record. Chrome offers it for a tab or the whole screen, not for a single window.
It needs a licence, and it needs tab capture, which Firefox does not provide. Open the recorder from the toolbar button while the tab you want is in front.
Some browser builds have no AAC encoder and put Opus audio inside the MP4, which a few players refuse. VLC plays it, and choosing WebM avoids it entirely.
That is the failure worth reporting, because the matching is the product. Tell us the site and the field label, and it can usually be fixed for everyone.
Deliberate. If no option clearly matches, it leaves the field alone rather than choosing something plausible — a dropdown keeps its previous value, so a wrong guess submits silently.
Fields inside iframes are not filled. Injecting into every frame would also reach advertising frames, which is a poor trade for something holding personal details.
Correct, and stated on the listing. The page is photographed rather than re-rendered, which is exactly why it works on pages you are signed in to.
Some pages redraw as you scroll, and the capture joins what was on screen. A narrower browser window often avoids it.
No extension can capture those, in any browser.
Reply to your purchase receipt, or use the support link on the store listing you installed from.