Permanent Parallels Desktop 18 license asking for upgrade payment

Hello,

I own a Parallels Desktop 18 for Mac - Standard Edition with a permanent (one-time purchase) license.

Recently, Parallels has started blocking my ability to run Windows and is requesting an upgrade payment,
even though:
• This is a perpetual license (not a subscription)
• I am not requesting any new features
• My Mac hardware and usage have not changed

I believe I should still be able to use the software version that corresponds to my purchased license,
but currently the application prompts me to upgrade in order to continue.

License details:
- License type: Permanent / One-time purchase
- License key (partial): 6J9BYT-*****-E67F74
- Purchase email: [email protected]

I've already contacted official Parallels support and sent a message via Facebook as well,
but wanted to also ask here in case there is a recommended version, workaround,
or clarification regarding the correct usage of a perpetual license.

Any guidance from Parallels staff or experienced users would be greatly appreciated.

Thank you,
David