TL;DR: return the Neewer TT560, and if you can, replace it with a Godox TT685 II-C. Or, in a pinch, an X2T-C transmitter and a Godox TT600.

The Neewer TT560 (which is actually a rebranded Godox TT560 and was also, for a while, the Amazon Basics flash) is what is known as a single-pin manual "universal" flash. It can only do the bare minimum of receiving the "sync" (fire) signal from a camera hotshoe and fire the flash. Nothing else. If you turn it over and look at its foot, you'll see it only has the one pin in the center.

Now look at the hotshoe of your 4000D (T100). It probably looks like this:

So the one signal a Neewer TT560 can receive from a hotshoe is the one signal a 4000D/T100's hotshoe cannot send. (Canon did the same thing to the 2000D/T7, and 250D/SL3).

The only Godox flashes that will work with that hotshoe are the TTL/HSS-capable ones, like the TT685 II or V1 that have pins for the remaining four contacts on that hotshoe and can communicate around the missing sync signal.

Alternatively, you can get the Godox X2T-C radio transmitter and mount that on the hotshoe, and that will give you a full five-contact hotshoe that can work with single-pin gear. But it's not a great match with a Neewer TT560, because the TT560 doesn't have any built-in radio remote control. A Godox TT600 is still single-pin and manual only but could also be used off-camera and communicate over radio with an X2T-C. And you'd not only be able to fire it remotely, but also have M power control and HSS (no TTL, though).

See also: What features should one look for when selecting a flash?