Purchase Request - not working

I was wondering if anyone could help me please. I work in the purchasing department and we currently have a paper document for colleagues to request Purchase Orders to be created on Sage, and we would like this process to become electronic. I have been looking on sage to see how this could be achieved and I think a Purchase Request should work – however, when I tested this out- it wouldn’t let me input the cost in the line amount (greyed out) and not all the suppliers we have on our system were 'allowed' to be input in the Supplier box. Any help would be greatly received. TIA