Add snippet for dynamic/conditional custom fields

[Zodiac1978]

I would like to add custom fields conditional to the chosen subscription (paid / free). If there is a paid membership selected the fields should be displayed. On free memberships these custom fields should be hidden.

I tried to achieve this, but without luck. Any help is much appreciated.

I wanted to change the button too, but as the button is not part of the Ajax response this seems to be more complicated than just the custom fields.