If Electrum is online, "Unpaid" status may have been a result of the received amount didn't matched your specified amount.
The issue here appears be the timing. OP has sent his request to expire at Unix time stamp 1607512999, which corresponds to 11:23:19 (UTC) on December 9th. The payment he received, which was for the specified amount of 0.006623, was not broadcast until 11:32 and not confirmed until 11:50, according to blockchain.com.
OP, the invoices you generate in this way are simply used by Electrum to track payments you have requested. If a payment is not paid within the time frame you specified, or pays less than you have requested, it will flag up as it did in your case here. That doesn't necessarily mean you have not received
any payment though, and payments can still be made just fine after your request has expired.