What is LOA (letter of authorization) when transferring a block of ipv6 addresses to a hoster?

Question

Computer networks

To the question
"I already have an Allocated/Assigned PA block-unit /48 ipv6
If I buy from you a dedicated server in USA, will you be able to route my ipv6 block to this server? Through your AS (Autonomous System).
Will I be able to use my ipv6 block on your server?"

Hosting support wrote the following
"We can provide this if you provide us a LOA"
What does this mean? and what do they want from me?

Answer 1

Still painted, why are you not guided by official documents ? You need to transfer your block to their AS, get a confirmation email from ARIN and send it to the host.
Will you ask a question on the toaster for each answer of your hosting TP?