555 5xx Server error RFC 8599
SIP 555 Push Notification Service Not Supported
The server does not support the push notification service the client requested.
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Common causes
- Mobile softphone requesting push (pn-provider) from a server that doesn't support it.
How to fix it
- Use a supported push provider or a push proxy.
Seeing 555 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 5xx responses
The server failed to handle an apparently valid request.