Are timing requirements in webRtc between calling setRemoteDescription and addIceCandidate?

I have implemented webrtc in 2 browsers that physically work on one local machine (one browser I will call as "local", another - "remote"). The browser - Firefox 112.0.1, TURN, STUN servers are not used.

All strings (offer, answer, ice candidates) are transferred from one to another browser manually (slow transfer - via copy and paste). "Remote" gets an offer from the "local" and processes it by rtc2_RegisterRemoteOffer (see code below). This function creates answer of the "remote". Then: (1) the negotiationneeded event fired on the "remote", (2) because of (1) "remote" creates offer and generates it's own ice candidates (up to here neither "local" nor "remote" ice candidates I didn't transfer to each other). (3) Then after few seconds on the "remote" iceconnectionstate fired with the status failed.

The questions are:

1. What may be a reason of iceconnectionstate gets failed - see (3) ?
2. Could this happen because I didn't have enough time to send any ice candidate from the "local" to the "remote" after sending offer ?
3. Is the case (2) - is correct behavior ? Should the "remote" create your own answer when it processes the answer of the "local" ?
4. If it shouldn't (question 3), then how the "remote" should correctly process it's own negotiationneeded event ?

The code of the "rtc2_RegisterRemoteOffer"

   function rtc2_RegisterRemoteOffer(remoteOfferText) {
        // Register an offer of a remote machine..
        // Input:
        //      - remoteOfferText - string - offer text.

        let stateStr = webRtc.peerConnection.signalingState;

        let logMsg = "rtc2_RegisterRemoteOffer is called. State = " + stateStr;
        DisplayLogMessage(logMsg);
        console.log(logMsg);

        console.log("==remoteOfferText==" + remoteOfferText);
        console.log(remoteOfferText);
        remoteOfferObj = {type: "offer", sdp: remoteOfferText};
        let remoteDescr = null;
        try {
            remoteDescr = new RTCSessionDescription(remoteOfferObj);
        }
        catch (e) {
            remoteDescr = null;
            DisplayErrMessage("Can't create SDP. Errmsg = " + e.message);
        }

        if (remoteDescr === null) {
            // error - do nothing
            DisplayErrMessage("remoteDescr === null !!!");
        }
        else {
            // set remote description
            let remotedescrPromise = webRtc.peerConnection.setRemoteDescription(remoteDescr)
            .then(function Resolve_rdp() {
                let msg = "rtc2_RegisterRemoteOffer.setRemoteDescription -- fulfilled";
                DisplayLogMessage(msg);
                console.log("===> ", msg);
            },

            function Reject_rdp(e) {
                let msg ="rt2c_RegisterRemoteOffer.setRemoteDescription REJECTED. Msg = " + e.message;
                DisplayErrMessage(msg);
                console.log("===> ", msg);

            }
            );  // let remotedescrPromise =

            stateStr = webRtc.peerConnection.signalingState;
            DisplayLogMessage("rtc2_RegisterRemoteOffer - Creating answer for the remote. State = " + stateStr);

            // create an answer to the remote offer

            let answerTextPromise = webRtc.peerConnection.createAnswer().then(
                // resolve
                function resolve_createAnswer(answer) {
                    // answer is generated

                    stateStr = webRtc.peerConnection.signalingState;
                    let msg = "rtc2_RegisterRemoteOffer.createAnswer - resolved. State = " + stateStr;
                    DisplayLogMessage(msg);
                    console.log(msg);
                    // (***) HERE I get:
                    // rtc2_RegisterRemoteOffer.createAnswer - resolved. State = have-remote-offer
                    // set the answer as the local description
                    webRtc.peerConnection.setLocalDescription(answer,

                        function resolve_setLocalDescription_answer() {
                            // resolve -- local description is set
                            console.log("===> ", "rtc2_RegisterRemoteOffer.SetLocalDescription fulfilled.");
                            // ----------------------------------------------------
                            // (***) HERE I get: the message above
                        },
                        function reject_setLocalDescription_answer() {
                            // resolve -- local description is set
                            console.log("ERROR = (setLocalDescription in rtc_RegisterRemoteOffer) is REJECTED");
                        }
                    );
                    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

                    // Display local answer for the remote
                    PutLocalAnswerText(answer.sdp);
                    DisplayStatus("Send answer to a remote");

                    // --- try to add local audio/video tracks to the remote ---
                    let tracksAdded = rtc2_addTracks();
                    if (tracksAdded) {
                        // our tracks sent to the remote
                        let msg = "rtc2_RegisterRemoteOffer_Our tracks sent on remote answer.";
                        DisplayLogMessage(msg);
                        console.log(msg);
                    }
                    else {

                        // can't access <mediaDevices>
                        let msg = "ERR1 - rtc_RegisterRemoteOffer_Our tracks WERE NOT sent on remote answer.";
                        DisplayErrMessage(msg);
                        console.log(msg);
                    }

                },
                function reject_createAnswer(e) {
                    let msg = "rt2c_RegisterRemoteOffer.createAnswer - REJECTED. Msg = " + e.message +
                                " State = " + stateStr;
                    DisplayErrMessage(msg);
                    console.log(msg);

                }

            );
        } // if (remoteDescr === null) else

    }   // function rtc2_RegisterRemoteOffer

The offer of the "local"

v=0
o=mozilla...THIS_IS_SDPARTA-99.0 672388715268626096 0 IN IP4 0.0.0.0
s=-
t=0 0
a=sendrecv
a=fingerprint:sha-256 65:F6:31:2A:FF:DD:7C:E1:89:83:C6:F1:8C:61:25:8F:E4:AD:0A:B6:8A:A7:D0:A3:0E:E0:DF:C8:99:5F:85:73
a=group:BUNDLE 0
a=ice-options:trickle
a=msid-semantic:WMS *
m=application 9 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 0.0.0.0
a=sendrecv
a=ice-pwd:e0e9063fdcde2bd9f4c3068accca0907
a=ice-ufrag:4386e8e0
a=mid:0
a=setup:actpass
a=sctp-port:5000
a=max-message-size:1073741823

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