I'm quite certain it's a scam. They will need to gain access to your computer though, maybe by tricking you to run some React app (or any executables). Have they told you to open/download something?
Edit: I forgot to tell that doing payments outside Upwork is a bannable offense so just flag them and move on.
Thank you for reaching out. Radia is correct, payment transactions in any form outside Upwork is against ToS and could get your account suspended.
We highly suggest reviewing our ToS, reading these tips on how to avoid questionable jobs, and this post from our Community member, Wes, about top red flags for scams for you to keep yourself safe in the marketplace. Should you also encounter any suspicious user activity again in the future, please send us a flag so the dedicated team can review it and take action as soon as possible.