Possibly Unhandled Rejection message when sending IM to a contact with node.SDK

Hi,
I'm trying to send a simple message to an IM session from a node.js app using the corresponding NodeSDK. I'm testing with two options:

Option A: sendMessageToJid API

Option B: sendMessageToJidAnswer API

Both options send the message to the contact, of course, option B is an answer from the previously received message.

However, with option A, with every message, I receive the following in the console:

  Possibly Unhandled Rejection at: Promise Promise { <rejected> undefined } reason: undefined

I get the same no matter if I include then/catch for managing Promise rejections or if I complete all the items in sendMessageToJid API, for instance:

sendMessageToJid('This is a message', message.fromJid, 'ES', null, 'subject')
or
sendMessageToJid('This is a message', message.fromJid, 'ES', 'text/markdown', 'subject')

What am I forgetting? Is this normal?

"rainbow-node-sdk": "1.69.0"
node.js: v12.16.1