Short answer: use “blink1control-tool” instead of “blink1-tool”!
Only one program can access the blink(1) device at a time. If running the Blink1Control app, you can either use the Blink1Control HTTP REST API or use “blink1control-tool”, a command-line program that has the same command-line switches as “blink1-tool” but does so
You can find “blink1control-tool” in the blink1-tool releases page. (You may need to scroll down, it doesn’t need updating as often so it may be on an older releases section)