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Unknown value in milestone payload
I'm exploring the following milestone message.
And I'm using the following RFC: 0019-RFC
From the message, I've identified almost every element, but there is one that is not referenced in the documentation. The value is after the milestone essence.

Network Id: b77f44715e0b3014
Parents' Length: 06
Parents:
22c91093bb85edc93065b937fd1cacf0e3edb4d85090c5ba2d5f01df5e9475e4
6ef22c8c2dfdbc64d2e915fdbbf9ee22631d6f38cdbddec9c19dcb225dd59452
91a1062313db1a03cb6450f1073e21077b99e8c1dfbfdce07c3960fd399de598
a7dc23c0432f3d838df8c2017740db8eff481a654c29a515eb126cbd75a0891c
b0f4aefbed43a6b2c7d393ba7ee3c9f77c6e0192f06df01d6448e6eb67a1e513
c9801a093f789496f3f1bc20a00714decd60dfd33c598894545bfb09ebfcd358
Payload length: bf010000
Payload Type: 01000000
Index Number: 2af30300
Timestamp: b5f1b06000000000
Parents' Length: 06
Parents:
22c91093bb85edc93065b937fd1cacf0e3edb4d85090c5ba2d5f01df5e9475e4
6ef22c8c2dfdbc64d2e915fdbbf9ee22631d6f38cdbddec9c19dcb225dd59452
91a1062313db1a03cb6450f1073e21077b99e8c1dfbfdce07c3960fd399de598
a7dc23c0432f3d838df8c2017740db8eff481a654c29a515eb126cbd75a0891c
b0f4aefbed43a6b2c7d393ba7ee3c9f77c6e0192f06df01d6448e6eb67a1e513
c9801a093f789496f3f1bc20a00714decd60dfd33c598894545bfb09ebfcd358
Inclusion Merkle Root: 0e5751c026e543b2e8ab2eb06099daa1d1e5df47778f7787faab45cdf12fe3a8
Next PoW Score: 00000000
Next PoW Score Milestone Index: 00000000
Keys Count: 02
Public Keys:
365fb85e7568b9b32f7359d6cbafa9814472ad0ecbad32d77beaf5dd9e84c6ba
a9b46fe743df783dedd00c954612428b34241f5913cf249d75bed3aafd65e4cd
Unknown value: 00000000
Signatures Count: 02
Signatures:
988a5221f5088165699557a8d982d4d3edad8ae23cc8880d0f4d655b876b06080077b0141eb505992d6fda43d1ddf12be4d57ac3e8399f55d55075edadb28804
b6858eb8a2b4ecac0ed40f52a250ad008b43fc1e761728a03929590660c4ca7dc6225e9e5bedf429eb82de97e35825be34066aaaf2d452fbc3fd5656b5e1590e
Nonce: f12a4f9224499224

Does anybody know what this value means? In the documentation the value before the signatures count value is the public keys array, so I don't know what this 00000000 is.
Thank you very much!

The unknown value is a uint32 used to determine if there is an optional receipt payload as part of the milestone payload. The receipts are for the transactions that were transferred from the legacy network.
If the value is 00000000 then there is no receipt payload included in the milestone, if it has a value of 00000003 the data that follows will be the receipt payload structure.
The RFC that describes the receipt payload can be found here https://github.com/luca-moser/protocol-rfcs/blob/rfc/wotsicide/text/0035-wotsicide/0035-wotsicide.md#receipts

Thank you Martyn, I've downloaded the message as a JSON file and I saw the receipt value as null, so I though that should be the 00000000 but I wanted to confirm it here ;)
