Hey @nhassan,
I dug into this and found the issue regarding the getIndex operation.
The UI does not generate the correct JSON for getIndex, the key for where the pattern is stored is generated as patternGetIndex. Changing this key in the advanced editor tab to Pattern will give you a valid index given that the regex is correct.
I am going to create a bug ticket to get this resolved, but for now you can use this as a workaround.