I have a pivot table, in Google Sheets, and want to add a percentage column.

EDIT: here is a link to a sample spreadsheet: https://docs.google.com/spreadsheets/d/12qyhOtKphW1iBWAOtfDHU1RdZRZ_Nq91eQtdghZzIyc/edit?usp=sharing

Below you can see the pivot table with the column (E) that I've manually added next to it, showing what I want to achieve, but as part of the pivot table, which is a simple:

E4=D4/C4

However, I have tried adding a Calculated Field under Values but can't work out the right formula; this didn't work:

='Checked In'/'Events'

nor did:

=D4/C4

I'm sure it's something simple, but I can't for the life of me work it out. Can anyone shine a light on what I'm doing wrong please?