How to specify a regular expression in a property checkpoint in a keyword test

This regex will match your string:

(\d{2}\/\d{2}\/\d{4}) (\d{2}:\d{2}:\d{2}) - (Attempting to connect to DMM\.)

Please remember that  / delimiter (as well as another delimiters) always should be escaped by backslash \

Also it is better to escape the dot character: \. Otherwise it will match any character.

And if you group different logical members of your string inside parentheses, it makes your regex more readable.

Great online tool to check your regex: https://regex101.com/