Vegas Pro serial numbers are for specific versions only. A serial number purchased for Vegas Pro 15 will only work with Vegas Pro 15, not with any earlier or later version. If you want to get a later version of Vegas Pro, you will need to purchase a serial number specifically for that new version - you may even be eligible for the upgrade pricing. Or you may wish to subscribe rather than making a new purchase. See https://www.vegascreativesoftware.com/us/vegas-edit/ for pricing.
Well the serial number I purchased was for Vegas pro 19 and I put it for Vegas pro 15. Is there anyone I can get in touch with than can help me or give me a refund please thank you
VEGAS Pro 15 hasn't been on sale for years, so I don't see how you expected to buy one for VEGAS 15... just use 19 if you've already bought it, it's way better than 15 anyway.