Pay something

-"There were," said he, "one or two VERY remarkable things. Perhaps when I have finished at the police-station you would care to come out and give me your opinion of them."
In am entirely at your service," said Sherlock Holmes, ringing the bell. "You will show these gentlemen out, Mrs. Hudson, and kindly send the boy with this telegram. He is to pay a five-shilling reply."

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Does it mean SH wants the boy to send the telegram, at the same time paying the money FOR the reply telegram that the prospective recipient is going to make?

Thank you.