Error when opening pgAdmin 4 on mac

Question

I have installed version 4-1.5, but when opening it, it always shows this error \"The application server could not be contacted.\"

Answer 1

I removed the local directory hidden and resolved:

$ cd ~
$ rm -r .pgadmin/

Note: macOS Sierra (10.12.6) and pgAdmin 4-1.6. Also you are going to loose configuration data like database list tree, et al.

The Databases will remain intact since you are modifying/deleting PgAdmin related data not any of Postgresql itself.