You need a nest which the single Magpie helped to build.  If you don't have one, you'll need to build one first which you can then use for magpie chicks.

oh I didnt know thanks

Unfortunately the one you've put out now still won't work, as it was added to by a pair of Magpies and not a single one.

You’ll need to start a new nest if you don’t have one with the regular magpie, every 5th spotted in your garden builds onto the nest so you’ll need to do that and then have 4 other birds of your choice to build the rest of the nest until complete. Once you’ve had your 10th bird spotted it will nest so if you have had 100 spotted in yours for instance you’ll need your next closest of the 10th so 110th magpie will then nest once spotted in your garden.

Aw, just put out a couple of empty nests and some veg, get the mallard to kick them off, then birdseed for phoenix, griffin, magpies, magpie pairs. Soon get yourself a couple of magpie nests. Make sure you not attracting any other birds xxx

Sorry. No pink cap during the mallard phase, then plant yourself a pink cap!