You need to identify which USB port you are using on the Mac and then edit the script accordingly. Also ensure the port is not open in the Ardiono IDE (or any other programs you have running that might be accessing that USB port).
i have similar problem but this is no solution for me
I have problem with instalation and find this tutorial on instructables.
HERE
but nothing works
Try using elevated rights, e.g. with sudo or run as root. The permission denied implies not enough rights. You could also make the cu.usbmodem file member of the group wheel I think but not sure.
Are you sure that is the name of your serial port? It says “file cannot be found” ?
I think i use 1410. This is from Arduino IDE. 
And when i try this port i got this.
I am new in arduino world and trying to catch up.
You need to select cu.wchusbserial1410 instead of tty.usbmodem1410 in your script.
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@Dmitriy i try but ddidnt work for me.
I came to solution but i have new problem. On my macbook pro i have 2 usb ports, the first is 1410, and the second is 1420. in blynk-ser.sh i change COM_PORT to mine cu.wchusbserial1420. On this port now i can work with Blynk, BUT i cant upload sketch from Arduino IDE. This is eroor.
So i CAN upload sketch on USB 1410 but i CAN’T run Blynk on it,
and i CAN’T upload sketch on USB 1420 but i CAN run Blynk on it.
Thanks for all help giveing to me.
Well, this is not Blynk problem itself. This is often happens with Arduino IDE. You may try to restart it, usually helps for me.
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Thanks man.
When i reset mac, USB start uploading sketch but Blynk didnt work. When i recieved wifi or ehternet shield or board i will play with Blink. This USB is killing me.
Yeap, USB is hard. It is nice to have ability try when you have no shield but for real-world cases it is better to buy appropriate shield.
i have a similar issue i get to that stage and then i got sucked seems like its not connecting to blynk - closed port?
2020/04/03 02:56:12 socat[12439] N opening character device “/dev/tty.wchusbserialfd120” for reading and writing
2020/04/03 02:56:17 socat[12439] N opening connection to LEN=16 AF=2 45.55.96.146:443
2020/04/03 02:56:17 socat[12439] N successfully connected from local address LEN=16 AF=2 192.168.1.4:59179
2020/04/03 02:56:17 socat[12439] N trusting certificate, commonName matches
2020/04/03 02:56:17 socat[12439] N SSL connection using ECDHE-RSA-AES128-GCM-SHA256
2020/04/03 02:56:17 socat[12439] N SSL connection compression “none”
2020/04/03 02:56:17 socat[12439] N SSL connection expansion “none”
2020/04/03 02:56:17 socat[12439] N starting data transfer loop with FDs [5,5] and [8,8]
Reopening really old topic instead of creating new one… bad 