The left clip is needed when neither of the fabric seats is in use - so in the following configurations:
2x carrycots plus (in any mode)
1x carrycot plus (in any mode) and 1x joey
1x carrycot plus (in any mode) and 1x infant car seat
1x joey and 1x infant car seat
**We have two versions of the clips - 2019+ and pre 2019, so ensure that you request for the correct ones for your carrycot plus/buggy.