I hope you are well and safe!
both SMI and request API does not support Multipart form data, so you cannot send the data from app.js through SMI or send the data from server.js to the third party API, I also have a question
why does the data need to go from server.js to the third party API, why not use ajax or fetch and send the data directly to the third party from the front end? if your concern is CORS issue, please refer this topic
Have a good day