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The backgrounds from kartverket (I mostly use “Kartverket Topo” parallel to Norway Orthophoto) doesn’t work for some days.
At first the download became slower and slower, then only this appeared:
Error downloading tiles…
My System is:
JOSM 19396
Java 21
Linux openSUSE 15.6
(same problem in Windows)
How can the problem be solved?
The URLs have changed slightly (now https://cache.kartverket.no/v1/service instead of https://cache.kartverket.no/v1/wmts).
The JOSM index is fixed, while the iD index remains to be corrected.
Thank you for integrating this alternative service into JOSM. 
Thanks for the information.
I hope the data will be available to all users again soon. 
I made a PR for iD’s layer index: Update URL for Kartverket topo by harahu · Pull Request #2705 · osmlab/editor-layer-index · GitHub
