Hello,
Altium flags this error if it finds that there is only pin connected to particular Net.
This is nothing incorrect technically about your design since you will be using J1 to connect the +3.3V supply and you know that.
At times, when a big design is being worked up the designer forgets to add the nets to pins, where in this check of Altium really helps to identify the issue.
Example,
You are working on 20 page schematic and with a 1000 Pin FPGA pins.
On schematic Page 1 there is a output signal "Sig_A" which is supposed to trigger some circuit which is on schematic page 15.
While working you missed to connect the Input pin on page 15, During validation Altium will show this error and you can easily rectify that.
You can hide this error in Altium setting.
Refer :
https://www.altium.com/documentation...nly-one-pin-adThanks.