Are you using the 'Vampire the Masquerade 5th edition by Roll20' character sheet? If so, that API is not built for that sheet. It's only for the sheet called 'Vampire the Masquerade 5th edition'. I know that might be confusing and if this is the case, it's probably the cause of the issue. The latter sheet is the one I personally use and I find it to be much more robust than the Roll20 sheet. That said, it's not official and it will not accept compendium entries. I can verify that API does work for the sheet its intended for. It should look like this.