Another thing to check - the trunk that connects the fax call to your Edge has to support T.30 fax protocol. If you are on PureCloud Voice, you should be fine, but if on another carrier or using a gateway to connect calls to your Edge, make sure that protocol is supported.
If you are using an FXS gateway to connect the Analog fax to PureCloud, see the article at
https://help.mypurecloud.com/articles/add-analog-fax-machine-purecloud-telephony-system/
(which also mentions Note: The connection to the PureCloud Edge requires a SIP interface using a UDP or TCP protocol that support g.711 mu/a-law media. The Edge does not support SIP fax over T.38. )