Cannot buy certain symbols via API

Using provided node sdk.
Paper trading atm.
Using fractional shares.

Creating orders with most symbols works just fine. e.g. VTI woks just fine. No errors, and the order is filled in my account overview.

However, some symbols result in a 403. Like SPXU.
Error text: “Request failed with status code 403”

Anyone know why only some symbols would fail?

I thought maybe some symbols would require limit orders, but get the same 403. All other leveraged ETFs I’ve tried also work fine. Just SPXU so far.

I can buy SPXU through the account interface using full shares no problem.

Buying full shares does work via API. So there is some issue with fractional shares and SPXU it seems.

Seems that some assets are just not “fractionable”. Bummer.