@AbdJabbar Hi there,
For this issue, your best move is to first get Autodiscover and EWS working using the Remote Connectivity Analyzer (a.k.a. RCA, https://testconnectivity.microsoft.com -> "Exchange Server" tab, use this one: "Microsoft Exchange Web Services Connectivity Tests", and use the Autodiscover option).
Note that the RCA used to use different IP's than Exchange Online, so your firewall had to also allow the RCA IP's in via HTTPS to your Exchange Autodiscover/EWS servers. This is no longer documented so I would say at least make sure that you have allowed the EXO IP's in the 1st row of this table (ID 1):
You should be able to succeed on the RCA before you bother trying to setup the migration endpoint, especially if you've tried and failed with the latter already.