Thanks for following this thread, @md gee. I'll share some information with you on how QuickBooks activation works.

You'll want to re-register discontinued products if they've been registered before on any computer and are being reinstalled. Thus, it keeps asking for registration after you reinstall your QuickBooks Desktop Point of Sale (POS) 19.0.

While working with Intuit representative, have you tried disabling your antivirus software temporarily? As it may be interfering with the registration process. Check out the outlined steps below:

1. Close all programs that access the internet or files from the internet, including email.
2. Locate your antivirus software.
3. Select Disable (or a similar option) to turn it off.

Additionally, when you’re asked to verify your information, make sure you provide similar details you did during the purchase. It should entirely match to prevent issues and difficulties while registering. 

Since the program won’t accept the activation code, please consider contacting our support team once more. Our representatives can find more solutions and help stop this threat.

In case you need migration guides and explore the Shopify POS solution, you can bookmark these websites for reference:

• Discontinuation of QuickBooks Desktop Point of Sale FAQs
• Shopify POS

You’re always welcome to get back on this thread if you need further assistance managing your program. Just add them to your reply below. I'll be here. Take care!