re: "The client wants me to deliver a fixed price job through an app, out of Upwork platform."
Doesn't really matter what the client wants you to do. Doesn't matter if it is an app, and doesn't matter if it is fixed-price or hourly.
"Out of Upwork platform" is against the rules.
You could have your account suspended if you mess around with that sort of thing.
Maybe the client is new and doesn't know this is against the rules.
You may politely decline to work off platform, and tell the client "Yes," you will be willing to work on this platform if she sets up an Upwork contract.
If she persists, then it means she is scammer of one sort of another. And you should flag her or report her.
Nuria, do you mean do the work and be paid outside of Upwork? That's a no-no as Preston said. However, if you mean deliver in the sense that you'd be delivering work product (files, etc.) via a method outside of Upwork that's allowed. I regularly deliver files to clients off platform, but include a message here on the platform including when and how the files were delivered. That way there's a record on-platform of the delivery.
Melissa: Excellent catch, and great clarification.
I didn't notice the possible other meaning of the original poster's question.
Nuria: As long as a client pays you through Upwork, it doesn't matter how you send files to the client.
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