Background Sign Caution

I want to wrap several commands into one line format to put in command/args field in yaml file for Kubernetes. But always get syntax error with bad ;, for example: -bash: syntax error near unexpected token ;', finally understand the error is from &.

Notice that here & should not have ; after it:

(echo 123)&; sleep 5; echo 456

Instead the correct way is:

(echo 123)& sleep 5; echo 456