AWS RDS: Invalid max storage size for engine name postgres and storage type gp2: 198

Your picture shows a maximum storage threshold of 198GB and usage of 197GB. According to this page the "The maximum storage threshold is the limit that you set for autoscaling the DB instance. You can't set the maximum storage threshold for autoscaling-enabled instances to a value greater than the maximum allocated storage.

Based on that it looks like you have set up autoscaled storage but have hit the limit you set. Modify your database to increase the limit and the problem should go away.

If that doesn't work maybe try increasing the database size by a larger increment.

Its because the max storage size for auto-scale will be at least 10% of your actually size 217 GB.