Thanks for the reply , yesterday I just created 1 user which is SQLMIRROR and when I created Mirroring I grant permission for that user ( as service account ).

So in SQL server services I changed Log on SQL server and SQL server agent as SQLMIRROR ( applied to both servers)

Also I added that user to master database ( applied to both servers)

When I check the permission level I can see the endpoint there

endpoint_MirrorGXYZ\White.LotusCO XYZ\White.Lotus

TSQL Local MachineGsaCO public

TSQL Named PipesGsaCO public

TSQL Default TCPGsaCO public

TSQL Default VIAGsaCO public

UNFORTUNATELY I still got the same error .

Any idea please?