Alias only works in the shell it has been defined in
Aliases only work in the same shell where they were defined. Not even in a subshell we get when we run a script. (But if we sourced the script then it runs in the same shell.)
$ alias tweet=echo $ tweet hello hello
examples/linux/tweet.sh
#!/bin/sh tweet "Hello"
$ ./examples/linux/tweet.sh ./examples/linux/tweet.sh: 2: ./examples/linux/tweet.sh: tweet: not found