Transfer posting from wm store to wm store

Do you mean that you have plant 1000/Storage Location 0110/Warehouse 110 and plant 1000/storage location 0111/Warehouse 111?

If yes it may depend on the actual location of your warehouses - if you need to perform shipping (for example if you need to pay for the transportation services to a forwarding agent) you may consider using stock transport orders with shipping between the storage locations. The setup and the process flow (STO->Outbound Delivery-> Shipment->Picking/Packing->Goods Issue->Inbound Delivery->Putaway->Goods Receipt) is similar to the widely used stock transfers between plants except that you have this part:

Of course you need to ensure that you can create correctly the transfer orders in the issuing and the receiving locations (check the determination of storage type/bin etc.).

If you do not require shipping - for example if you can use internal transport for a few hundred meters to the next building and you don't need to plan this much in advance - you can use MIGO with 311 (one-step) or with 313/315 (two-step). Usually the two-step approach is a better option compared to 311 but this is up to the business to decide. This will generate transfer requirement in 110 which you can process via LB10 and LT21. After you post with 315 in 111 you will have another transfer requirement which again you can process via LB10/LT21.

Check the settings for your movement types and storage type determination in both warehouses, make sure that the bin for stock transfers in storage type 921 is created.