The headline is wrong. The right to use cash wasn’t even part of it. It was pretty symbolic overall.

The original popular initiative:

Die Bundesverfassung wird wie folgt geändert:
Art. 99 Abs. 1bis und 5
1bis Der Bund stellt sicher, dass Münzen oder Banknoten immer in genügender Menge zur Verfügung stehen.
5 Der Ersatz des Schweizerfrankens durch eine andere Währung muss Volk und Ständen zur Abstimmung unterbreitet werden.

My translation:

The federal constitution will be changed as follows:
Art. 99 Par. 1+ and 5
1+ The federal executive ensures that coins and bank notes are always available in sufficient amounts.
5 A replacement of the Swiss Franc by another currency must be put to a popular and cantonal vote.

The counter proposal of the parliament we eventually voted for:

Die Bundesverfassung wird wie folgt geändert:
Art. 99 Abs. 1bis und 2bis
1bis Die schweizerische Währung ist der Franken.
2bis Die Schweizerische Nationalbank gewährleistet die Bargeldversorgung.

My translation:

The federal constitution will be changed as follows:
Art. 99 Par. 1+ and 2+
1+ The Swiss currency is the Franc.
2+ The Swiss national bank ensures the cash supply.

That’s literally the whole change.

Any ideas resembling forcing businesses to accept cash were dropped from discussion without making it into the proposal.

Edit: Here is a short version that’s even available in English on the Federal Council website: https://www.admin.ch/gov/en/start/documentation/votes/20260308/cash-nitiative-and-counter-proposal.html if you change the language in the top right to one of our national languages you can also download the PDF with the initiative text in the right sidebar, to verify my quotes.

Edit2: Added my translations

Edit3: In case anyone wants to know, I voted against both initiative and counter proposal. I just don’t see the point in a change without effect. Any change to national currency could already be overturned by popular referendum, if it was ever realistically proposed, whether it’s in the constitution or not. It just seemed like fear mongering by defeating a non-existent threat.