If you are unable to connect to Office 365 account, it is due to Microsoft Security setting. Make some changes in your account and allow access to our software. Follow the below steps for App Registration:
Step 1: Login to Microsoft Azure Portal
Step 2: App Registration - Manual Steps
Step 3: Show You App Registration
Note Application (client) ID and Directory (tenant) ID - it is required for Office MFA Login Time.
Step 4: Generate Certificates & secrets
Step 5: Add a Client Secret
Enter Description, select Expiry Date for validity, click Add.
Step 6: API Permission
Click on API permissions --> click + Add a permission.
Step 7: Request API Permission
Step 8: Request API Permission >> Application Permission
Step 9: Request API Permission >> Grant admin consent
Click Grant admin consent for "Your Organization Name" link.
Step 10: Request API Permission --> Grant admin consent confirmation --> click Yes.
Step 11: Request API Permission --> Grant admin consent --> click Refresh.
You can see here permission has been granted for your App.
Step 12: Enter Client ID and Tenant ID into Regain OST to Office 365 Login Portal.
Step 13: You can validate Login to Microsoft Open Dialog.
Step 14: Enter Global Admin Password --> click Sign in.
Step 15: App Permission Request
Select the checkbox Consent on behalf of your orgaization --> click Accept.
You will successfully login into Office 365 Global Admin Account.
If still facing any issue, then add Impersonation Rights in Exchange Admin Center (EAC).