Have you asked their support or about this?
Can you please post bet ID if possible and/or seeds?
Lazy people.
BetID: https://primedice.com/?iid=25136673921&modal=bet
Nonce: 424
Server seed(secret): 55bc50e043c2fba8124f7abeb9912b1362f9d04ebbf3da577fc87e543aa5ad85
Server seed(hashed): ce3b954cfc387a3910006c7d209a609b88db03ec309549b9f412c4085fa7e738
Use this tool to check server seed https://passwordsgenerator.net/sha256-hash-generator
As you can see, server seed is good.
Lets check result with this tool https://www.freeformatter.com/hmac-generator.html:
Well, before you get result, you need to convert first 5 characters from hexadecimal to decimal (use calculator) and you will get this number: 805099.
Little math from primedice:
Result is as you can see 50.99 and everything is fine.
Client seed bur34rr7676DODAM with the same server seed and nonce 424 will return this result --> 74.63