Depending on the RIR your IPs are issued from, your requirements for an LOA may be different. The following is an example for ARIN based IPs:
Please note we do require a validated IRR record authorizing our ASN to announce your IP block, and strongly encourage a valid ROA be signed as well.
AUTHORIZATION LETTER
[DATE]
To whom it may concern,
This letter serves as authorization for H4Y Technologies LLC with AS397373 to announce the following IP address blocks:
[IP SPACE / ASN / SUBNET]
[IP SPACE / ASN / SUBNET]
[...]
As a representative of the company [COMPANY] that is the owner of the subnet and/or ASN, I hereby declare that I'm authorized to represent and sign for this LOA.
Should you have questions about this request, email me at [E-MAIL ADDRESS], or call: [TELEPHONE NUMBER]
From,
[NAME]
[COMPANY]
[TITLE]
[TELEPHONE NUMBER]
