Why am I getting an error when serving an app extension with CLI?

[ThiagoMine]

Hi every one, I need some help!
I'm developing a post-purchase upsell app and I'm having some trouble on serve comand of CLI.

When I run:

shopify extension serve

I get:

> checkout-ui-extensions-template@0.1.0 server /home/thiago_mine/Code/CommerceDots-App/upsell_extension
┃ > yarn start "--port=39351" "--publicUrl=https://69d2-35-226-184-58.ngrok.io"
┃
┃ sh: 1: yarn: not found
┃ npm ERR! code ELIFECYCLE
┃ npm ERR! syscall spawn
┃ npm ERR! file sh
┃ npm ERR! errno ENOENT
┃ npm ERR! checkout-ui-extensions-template@0.1.0 server: `yarn start "--port=39351" "--publicUrl=https://69d2-35-226-184-58.ngrok.io"`
┃ npm ERR! spawn ENOENT
┃ npm ERR!
┃ npm ERR! Failed at the checkout-ui-extensions-template@0.1.0 server script.
┃ npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

┃
┃ npm ERR! A complete log of this run can be found in:
┃ npm ERR! /home/thiago_mine/.npm/_logs/2021-10-04T15_37_55_035Z-debug.log

Folllow a print: