I was able to replicate this when attempting to run /whitelist add on a player, I have also had issues with the bulk endpoint starting around the time of 1.21's release through modded server plugins calling it for name lookups, it gives a 403 fairly consistently (though not always). Interestingly, I have not had issues with the non-bulk endpoint. I am guessing some sort of WAF rule being too strict. Requests are being made from a datacenter in Virginia:
[17:07:01 ERROR]: Got an error with a html body connecting to https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname: <html>
<head><title>403 Forbidden</title></head>
<body>
<center><h1>403 Forbidden</h1></center>
<hr><center>Microsoft-Azure-Application-Gateway/v2</center>
</body>
</html>
[17:07:02 ERROR]: Got an error with a html body connecting to https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname: <html>
<head><title>403 Forbidden</title></head>
<body>
<center><h1>403 Forbidden</h1></center>
<hr><center>Microsoft-Azure-Application-Gateway/v2</center>
</body>
</html>
[17:07:03 ERROR]: Got an error with a html body connecting to https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname: <html>
<head><title>403 Forbidden</title></head>
<body>
<center><h1>403 Forbidden</h1></center>
<hr><center>Microsoft-Azure-Application-Gateway/v2</center>
</body>
</html>
[17:07:03 INFO]: That player does not exist
I was able to replicate this when attempting to run /whitelist add on a player, I have also had issues with the bulk endpoint starting around the time of 1.21's release through modded server plugins calling it for name lookups, it gives a 403 fairly consistently (though not always). Interestingly, I have not had issues with the non-bulk endpoint. I am guessing some sort of WAF rule being too strict. Requests are being made from a datacenter in Virginia: