Payload gets temMALFORMED response, but works fine in Payload Signing tool

https://xumm.dev/signing-tool?payload=5576ce40-b97c-40f6-89d9-1c926ac3feec&txid=2253AD15E1BEBC005D9138AD1EBB847487E4B9D73A7506FFAD3148BF492353A3

Above is an example of a successfully signed payload signed in the Payload Signing Tool.

This same payload gets a temMALFORMED error when I attempt to sign it via the jwt API from my app. The only difference is the addition of the redirect_url:

{
  "options": {
    "return_url": {
      "app": 'origami://?id={id}&cid={cid}&txid={txid}&txblob={txblob}',
      "web": 'origami://?id={id}&cid={cid}&txid={txid}&txblob={txblob}',
    },
  },
  "txjson": {
    "Account": "rhJ6HKU4rLXGEkKHXLRoL7B61XvLz9JCem", 
    "Amount": "1000000", 
    "CancelAfter": 743736082, 
    "Destination": "rhJ6HKU4rLXGEkKHXLRoL7B61XvLz9JCem", 
    "Flags": 0, 
    "LedgerEntryType": "Escrow", 
    "TransactionType": "EscrowCreate"
  }
}

Any ideas of what might be going on, or how to troubleshoot this? I am using the testate, but the signing tool doesn't seem to mind.