I noticed that the comma for the "expiredAt" value is missing, leading to issues. Easy to spot on an IDE, but thought I'd mention this.
If you look within the JSON.stringify({}) body, the "expiredAt: null" line does not contain a comma at the end before the new line "base: base.publicKey.toString(),".
The page with the error:
https://github.com/jup-ag/space-station/blob/main/docs/3-limit-order/1-limit-order-api.md