*ignoring bad CNAME "_gateway" for host "_gateway": domain name "_gateway" starts with invalid character*

When sending test.txt from my Linux Mint 22 Cinnamon Framework 13 to my Fairphone 4 LineageOS acting as a Wifi hotspot I am connected to.

scp -4 -P 8022 test.txt _gateway:/sdcard/test.txt

Output:

ignoring bad CNAME "_gateway" for host "_gateway": domain name "_gateway" starts with invalid character
test.txt                              100% XKB   9.0MB/s   00:00

While the file is correctly sent.

+20