It’s a metaphor for a musician. It means the musician (and his or her music)

in medieval times the piper played a pipe instrument like a litle flute (today it would be called a tin whistle, recorder or piccolo) and this apart from the drum was about the only instrument available to the common folk. The piper would lead the drums and the people in processions; in war; at fairs, and so on. ‘who pays the piper calls the tune’ is an old expression. The pied piper of Hamlin is alegend about a piper who led the rats out of a Hamlin and then led the children out (to their vanishment) when the town council refused to pay him. Pipes or ‘fifes’ still play in marching bands (think of yankee doodle for example)

The piper?

Reference to the Pied Piper of Hamelin, a man who was cheated after removing the towns rats. He then led their children away as revenge.

“The piper is calling you to join him” would fit that

or

Reference to being piped aboard a naval ship, as a high ranking officer or guest

I think it’s the one where you blow in it so you can tune an instrument.