How to resolve "enter the password for credential storage" issue?

So I am playing around with fiddler web proxy. I need to decrypt https traffic. So I am trying to put the fiddler root CA cert in my device trust store. But it keeps asking me "Enter the password for credential storage". If i enter anything and click enter I see an Toast message saying

Credential storage has been erased

and the password prompt comes again. This goes on in a loop. For the record I have selected "Wifi" as the Credential use instead of "App n VPN" (not sure of that matters).

Next wired thing that I noticed is that after each prompt the description changes for label

The package contains

The value for it increases each time the password prompt is shown. For eg - 3 CA certificates, 4 CA certificates and so on...

As much as I want my device to accept this certificate I would appreciate if someone could explain the "credential storage" concept and the weird increment of CA certs text.