What does the syntax "|&" mean in shell language?

From the bash man page:

Pipelines

A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The format for a pipeline is:

[time [-p]] [ ! ] command [ [|│|&] command2 ... ]

The standard output of command is connected via a pipe to the standard input of command2. This connection is performed before any redirections specified by the command (see REDIRECTION below). If |& is used, the standard error of command is connected to command2’s standard input through the pipe; it is shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any redirections specified by the command.

Check your hash-bang line. Plain sh doesn't support |&.