Reproducer to get into such error situation:
- Use external DNS server (we use Windows AD based DNS servers) and not the internal DNS servers of IPA
- Install a RHEL7 IPA server and have it working (we have it also AD connected, but for this case it does not matter)
- Confirm the SRV records point to RHEL7
- Install a RHEL8 server
- Switch on the external DNS the SRV records already tp point to RHEL8 server
- Install RHEL8 IPA server without the --server option to have it using the SRV records (that already point the the RHEL8 server that is  being installed)
- Run on RHEL8 ipa-server-install -uninstall to prepare to try again
- Install RHEL8 IPA server now with the --server=RHEL7-fqdn
- Now you have the failure that the replica-agreement already exists from the first installation that was failing because the SRV records were point to the not yet install RHEL8 IPA server

In our installation i found out that mentioned command on replica-agreement had to be executed on the RHEL7-IPA server where the agreement was also already created.

That means that the error is missing important information that the replica-agreement has to be deleted from the other end of the agreement.
Expected error my real-world use case, the information missing i added in <<...>>:
~~~
The ipa-replica-install command failed, exception: ScriptError: A replication agreement for this host <<new.server.example.com> already exists <<on working.server.example.com>>.
Run this command <<on workin.server.example.com to remove the replication agreement>>:
    %% ipa-replica-manage del new.server.example.com --force
~~~

Easy to fix. In ipaserver/install/server/replicainstall.py, in the method promote_check (line 1024), the installer looks for an existing replication agreement and prints an error message:

----- 8< -----
        # Check that we don't already have a replication agreement
        if replman.get_replication_agreement(config.host_name):
            msg = ("A replication agreement for this host already exists. "
                   "It needs to be removed.\n"
                   "Run this command:\n"
                   "    %% ipa-replica-manage del {host} --force"
                   .format(host=config.host_name))
            raise ScriptError(msg, rval=3)
----- >8 -----

The msg needs to be changed into "Run this command on any working server: %% ipa server-del {host} --force"
- ipa server-del instead of ipa-replica-manage del because only domain-level1 is now supported
- and the commands needs to be run on a working server, not on the host where ipa-replica-install failed

fixed upstream: https://github.com/freeipa/freeipa/pull/6274

Moving to POST.

Fixed upstream:
master:
https://pagure.io/freeipa/c/5457fb7f7efef368b4e6db44f644b909d14c3f44

ipa-4-9:
https://pagure.io/freeipa/c/c03a8c3c06562c128aac6be506274995cea74948

Test added upstream
master:
https://pagure.io/freeipa/c/ce50d2255f9f7adaebd221e462f75cbe79366d75
https://pagure.io/freeipa/c/94dd9ef1d69e30f687686d8584b6b79880a098f3

ipa-4-9:
https://pagure.io/freeipa/c/352b9dfb49bdf1c70a8de9ed7287387417580c86
https://pagure.io/freeipa/c/58ddcffc412f7dd5cc762bd6f80faa07fcedf7ec

Pre-verified using automation from ipatests/test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer:test_replica_install_existing_agreement with the package ipa-server-4.9.10-1.module+el8.7.0+15691+2b2c1dd5.x86_64

Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server_without_ca 	
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server_without_kra 	
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server 	 	
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_existing_agreement

Therefore marking as verified: tested. Full test log is an attachment of this BZ.

Verified using automation from ipatests/test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer:test_replica_install_existing_agreement with a package ipa-server-4.9.10-4.module+el8.7.0+15926+daa9f08b.x86_64 from the nightly repository.

Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server_without_ca 	
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server_without_kra 		
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_against_server 	
Passed 	test_integration/test_installation.py::TestInstallReplicaAgainstSpecificServer::()::test_replica_install_existing_agreement 	

Full pytest log is an attachment of this BZ.

Marking as verified.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (idm:client and idm:DL1 bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2022:7540