Developer Questions

When signing a transfer request in an app (currently in beta, using the nft-devnet), I get a popup saying:

Error
Unable to get network fee, please make sure you are connected to the XRPL node.

Any idea what might be going on? I'm omitting the transfer fee from the tx record, as suggested in the docs: https://xumm.readme.io/docs/payload-transaction-data#fee-transaction-fee

My transaction looks like this:
const request: XummPostPayloadBodyJson = {
txjson: {
TransactionType: 'Payment',
Destination: walletAddress
Amount: ${amount * 1000000} // 1,000,000 drops in 1 xrp
},
options: {
return_url: {
app: returnUrl,
web: returnUrl
}
}
};