I found this in another post and it solved my problem
This can happen if you use Wordfence:
1 – Look in WordFence tools – look for the item listed with a red dot (probably listed as /wp-admin/admin-ajax.php). Use the eye icon on the right hand side of the listing to view it. Then click “Add param to firewall allow list”.
2 – Then, for good measure, set Wordfence to Learning Mode. WordFence > All Options > Basic Firewall Options > Learning mode.
3 – Log in as a Vendor / Test vendor, edit a product and submit. All will be working fine.
