Build a Interal VBA macro interface

Problem: We have one internal website A were users go and perform upload tasks for vendors (All users have access to this website). However, before the team makes uploads they need to check if the (input )vendor code is a manufacturer or not from another website B. Due to teams not checking this 100% we have several incorrect uploads for non-manufacturers. Proposed solution: First, we want to restrict website A access for all users ( If there is a code?) . Then we want to build an excel macro which users will use where they will input data(vendor code). And then they will click go. This macro should first go to website A validate if the input is a manufacturer or not. If yes, should proceed to next website B automatically and make upload changes. If no, should give the user a pop up saying there is an issue so this is pro-actively addressed and does not proceed. Both websites are internal websites the only way I can think of getting access for anyone will be if we meet personall and you can work on my system to connect the codes.