Hi Laurent,
Was this DB working previously with the same setup? Did you change some settings on the DB side perhaps? Is the specified db definitely correct? If you try to run a simple SQL command to list all tables, does it work?
N.B the test connection button isn't always a 100% source of truth. We haven't rolled out any cloud releases or feature flags relating to PSQL resources in the last few days, so I suspect this is an issue with connecting to the DB itself.
If you switch to the schema tab (next to output) I suspect it will be empty, because the underlying connection is not working (despite the false positive from the test connection button)
I wrote a guide here to help troubleshoot these kinds of issues which should be helpful for debugging this: