Can I connect DTR Pin to CTS Pin?
Not a good idea.
Connect the CTS to CTS, and RTS to RTS. DTR is different. The FTDI has both CTS and RTS pins.
RTS and CTS are used for hardware flow control, its a way to say &quot;hey I'm going to send a message&quot;. Or if the pixhawk supports it, you could use software flow control and only use TX and RX. Whaever you do, make sure both ends have the same baud rate, stop bits, partiy and hardware flow control settings.

Source: https://www.mikroe.com/blog/uart-serial-communication