Both messages show up before the profile is installed. iPhone often says "Unable to Complete Cellular Plan Change". Android often says a carrier authorization error, or similar wording. The download was refused. That is not the same problem as "installed, but no data after landing".
Try this order
1Keep the exact message
Screenshot it or copy the full sentence. If this needs a manual review, we need the words you saw, not only "it would not install".
2Retry the same QR code on a stable connection
Downloading the profile requires a connection first. Wi-Fi or your existing mobile data both work. The order page and the email show the same QR code. After you change networks, scan that one again. Do not look for a second activation code.
3Confirm this phone can install a third-party eSIM
The device must support eSIM and must not be carrier-locked. A phone locked to a carrier contract cannot install a third-party profile. How to check: compatibility.
4Confirm this QR code was not installed elsewhere
One profile installs on one device. If it already installed on another phone, scanning again fails. A new code is not a way around that.
Do not delete it and try again
If the profile is already listed under cellular plans, do not delete it and scan again. After deletion it usually cannot be reinstalled, and "installed, then deleted" is outside the refund rules. If the line is listed and only the data is missing, use no signal after landing instead.
If it still will not install
If the profile never installed, and you already retried on a stable connection, confirmed the phone is unlocked, and confirmed the QR code was not used on another device, send the order number and the exact message through contact. A demonstrable technical fault — an invalid profile, or an upstream line that was never provisioned at the destination — is handled under the manual-review section of the refund policy. An unsupported device, a carrier lock, or the wrong destination is not refundable.