Admin can not Add Payment for Gateway unless client has used that GW.

I think this may be related to other issues; but hard to be certain.

I think the shortest way to explain this is as the titles states. When an admin goes in to Add Payment for an Order; they are only allowed to use gateways which have been already used by the client.

Originally admins could only use Methods used by the client. i.e. if a client used a CC (Auth.net CC GW) then for future orders for that client, an admin could only make payments using that CC. With this patch: #2912996: Support admin order payments admins can now make payments with a new CC.

But, admin still can't make payments with other enabled GWs.

For example, until a client uses a CC; they can't make a CC payment, although, i think with this patch #3015970: Adding a payment method is only possible for one gateway they may now be able to. But, for example:

- i have 2 other GWs enabled: PayPal and Manual
- Admin was not able to use either of these at first
- after Client used Manual (normally would not be allowed); then this was now available to the admins to make payments for this client
- PP was never used by the client; so not available to the admins

The main place, for us, that this becomes an issue is accepting checks. The Manual gw will not be enabled for clients; and therefore never shows up for admins when adding payments.

I am not sure how this has been missed up until now as this must be a pretty common procedure. And it would seem like a pretty simple fix - i am sure i will eventually take a look). I get that admin is loading payment "methods" that client ahs used (since it seems like a method is tied to a CC; but, not sure why this isn't simply merged with the other GW (gw's methods??).