When submitting a XFEL publication to DESY's PUBDB database, make sure the revant fields are filled properly according to this screenshot:

Note: Of course select the appropriate Groups(s) entry if more or different groups are involved.

XFEL Acknowledgement

In addition to following the DESY Publication guideline you should also acknowledge the European XFEL for your work. You can use one of the following suggestions:

"This work was supported by operation funds of the European XFEL"

or:

"This work was supported by funds of the European XFEL R&D program."