Google Cloud Nat One rule needs more IP addresses

[Abdellatif051]

I have a Cloud NAT with this config (fake adresses):

• Source subnets & IP ranges: All subnets' primary and secondary IP ranges
• Cloud NAT IP addresses: Manual: 203.0.113.30, 203.0.113.40
  
  I added a customized rule 1:
• Match: 198.51.100.20/30
• source_nat_active_ips: 203.0.113.20All network service tier are premium.

After I added this custom rule I have a status alert: Rule needs one more IP address.

There is no mention in the documentation that requires us to add multiple addresses in a single cloud nat rule.

Alert screenshot: 

Architecture screenshot:

Is that normal ?

Has anyone had this problem before?