You need the Saturday. They have a maybe. Your assistant wrote a warm introduction to the artist. They book rooms, not biographies. The biography can wait until the hold exists.
A hold is a decision with a clock. Write the clock where the office manager can find it.
Date, room, hold or release
Name the decision. "I need you to hold 12 April in the small room until the 20th, offer the 19th instead, or release the 12th." Give the show as the audience would see it, expected headcount, and the one technical constraint that kills a room — a load-in they cannot do, a curfew, a standing-only policy you will not take.
Do not attach the rider. RelayLink does not carry attachments. Describe the rider in the briefing. Send the file on the channel they already use for riders.
One date per message unless you are asking them to pick between two named nights. A tour routing in one email is a call.
Write for the inbox that is not the person you drank with
Venues are often not on RelayLink. The booking address may be a shared mailbox. Write so a colleague who has never met you can file the request. You assumed the room still has the same capacity. You assumed the in-house sound is what they advertised. You assumed the hold they mentioned on the phone is still open. Label those.
Use the room name they publish. A nickname you keep for the buyer stays on your side.
You approve it; they reply from the office
You review the wording. They do not need an account. The briefing arrives as email. They can reply there. If that address already has an activated account, you need an accepted pair for a new thread. The refusal will not tell you which.
Say what you will do if you do not hear by the date you named — move the hold request to the other city, or drop the night. Honour it. A decorative deadline is how you become the booker they ignore.
If the venue wants a deposit or a contract next, that is a later message on the channel they already use for paper. This briefing is only the hold. Mixing the two is how a date question becomes a packet nobody opens.
After they answer
Write back the hold in their words — date, room, until when — and ask them to correct that sentence. Then stop shopping the same night as if it were open. If you need a second room, that is a second ask.
The show can still fall over later. This message is the night you are actually holding.