Upwork changed their policy recently
As Upwork doesn't provide lasting value, yet seeks to make money on lasting connections, they have now made it against their terms to even discuss the project outside of Upwork before a contract gets started on Upwork. Therefore, when you see the upcoming lectures on using Calendly to make it easier to schedule meetings with clients, you'll want to consider if it's worth it to you to make sales faster and easier, while risking having your Upwork account suspended due to Upwork's ever-increasing madness that hurts everyone on their platform.
If you don't want to risk your account, then a safer solution might be to give the client 3 different dates and times you are available, and asking them to select one. Plus, instead of using convenient contact methods, such as phone or Skype calls, you'll need to use Upwork's built-in speakerphone-based "Call" feature. It's far from ideal, but it protect's Upwork's profits above all else.
Upwork's system is now configured to automatically attack anyone (even after a contract started) who even remotely suggests that they may be talking to anyone outside of Upwork. Notice that I was discussing the client paying with PayPal in sandbox mode on their own website to test the work I built for them. This fascist bot message showed up moments later with the word "PayPal" highlighted. (The message automatically highlights "PayPal" and gives you a popup with a similar message trying to attack you for doing your job. I didn't highlight that text.)
Be safe guys. The fascists at Upwork destroyed me financially by stripping away our agency's "Top Rated" status about a year ago, and our agency brought them tens of thousand of dollars. They care nothing for the people on their platform and will destroy you if it suits them, or even when it doesn't. It's not about money with them; it's about power. Increase your funds through them, then start an agency or another business so that you can leave them as soon as possible. They're a means to an end.