Step 1: Login into your Microsoft admin panel using your admin credentials.
Step 2: Under Admin center, navigate to Settings option.
Step 3: Under Settings menu, click on Org Settings.
Step 4: Under Org Setting, go to Security & Privacy section.
Step 5: Under Security and Privacy section, click on Sharing option.
Step 6: Make sure guest access is enabled, and adjust the permissions as needed.
Step 7: Finally, click on save to apply the changes.
