I'm trying to use lt3467A in sepic configuration. Using ltspice, it seems possible, but my prototype does not work
Where is my error?
The error has to be in your hardware, as the simulation should run fine modeled as the schematic you're posting.
There is just one problem with your simulation: even though it runs fine, the switch current is too high. For a 5V input and an 8V output the guaranteed switch current is very close to 1A.
If you really need about 270mA, as suggested in the simulation, you need to use 2.2uH coupled inductors (both windings on the same core), or increase both inductors to 4.7uH.
Or, simply reduce your load.
That however, will not fix the hardware issue.