Without knowing anything about your case, it’s possible that the serial number is for the correct product but for a different licensing type and to fix things you just have to find the correct installer for the product that matches the license type.
What product is the serial number supposedly for and/or what product are you trying to install?
What license type is it: individual, academic, student, teacher, enterprise, government, teams, cloud?
Do you have a chat transcript that you can review again, privately, to help determine what license type the serial number is for?
Don’t post your serial number, here, in its entirety or even most of it, because this is a public forum, but can you give us the first 4 digits (of the 24 digits) because some Adobe products, at least, have the same four digits for each product serial number at least of a specific license type and sometimes for all license types, and that would help validate whether the serial number you’ve been given matches what you’re trying to install. For example, all recent Lightroom serial numbers for the Individual license type start with the four digits 1160.